text stringlengths 454 608k | url stringlengths 17 896 | dump stringclasses 91
values | source stringclasses 1
value | word_count int64 101 114k | flesch_reading_ease float64 50 104 |
|---|---|---|---|---|---|
Did you try Tools>Build?
I wrote this code,
#include <stdio.h>
int main()
{
printf("Hello world\n");
return 0;
}
I went to Tools -> Built. Then came this message.
"/Users/mohamedsuhail/Desktop/program.c:1:19: error: stdio.h: No such file or directory
/Users/mohamedsuhail/Desktop/program.c: In function 'int main()':
/Users/mohamedsuhail/Desktop/program.c:5: error: 'printf' was not declared in this scope
[Finished in 0.0s with exit code 1]"
Someone please help so i can continue using Sublime Text 2 for C. I don't want to use another program.
This isn't a problem with Sublime Text, it's your development setup that's incomplete.
For OSX, you need XCode installed, then run
xcode-select --install
to install everything needed.
You could use Sublime Text's build system, but I wouldn't recommend it until you learn your way around the command line. To build, cd into your source directory and use
cc -o program program.c | https://forum.sublimetext.com/t/how-to-run-the-program/12127/6 | CC-MAIN-2016-07 | refinedweb | 164 | 70.19 |
foreach vs for
I’ve just hit the foreach code coverage issue again in one of my unit tests (see my Code coverage doesn’t like foreach loops post). To ensure that my tests were correctly covering all possibilities, I had to change the foreach loop into a for loop and run the test again.
The issue in this case is that the collection object I was referencing was ConfigurationElementCollection which implements ICollection. Unfortunately, this type doesn’t expose an indexer property. In order to test the code coverage metrics using a for loop, I first had to create an array of the appropriate length and copy across the items across.
After running the test again, I had 100% code coverage. I have now confirmed that the missing blocks in coverage are a result of the foreach statement rather than an issue with my unit test. Now the question is do I remove the additional code and redundant array copy ? The reasons to convert the code back to the foreach loop are:
- Cleaner code
- Less bloat
- More understandable
- Code coverage shouldn’t define coding style
The second point is guaranteed to get some people in a flap. To be clear, I am not saying that testability shouldn’t have a bearing on coding style, I’m saying that code coverage shouldn’t define coding style. While this post is about code coverage, I should also point out that code coverage doesn’t really mean much by itself. It is just an indicator.
In this case, the unit tests were valid and covered all the angles, so the question is purely whether a code coverage metric is important enough to modify the code.
Another thing also comes to mind. What about performance? By using the array, I have the additional overhead of creating an array and populating it from the ICollection, but then I have the performance gain from not using the IEnumerator invoked by the foreach statement.
A quick test gave me a suitable answer.
using System; using System.Collections.ObjectModel; using System.Diagnostics; using System.Threading; namespace ConsoleApplication1 { internal class Program { private static void Main(String[] args) { Collection<String> items = new Collection<String>(); for (Int32 index = 0; index < 10; index++) { items.Add(Guid.NewGuid().ToString()); } Stopwatch watch = new Stopwatch(); const Int32 Iterations = 10000; Thread.Sleep(1000); watch.Start(); for (Int32 index = 0; index < Iterations; index++) { foreach (String item in items) { Debug.WriteLine(item); } } watch.Stop(); Console.WriteLine("foreach took {0} ticks", watch.ElapsedTicks); watch.Reset(); watch.Start(); for (Int32 index = 0; index < Iterations; index++) { String[] newItems = new String[items.Count]; items.CopyTo(newItems, 0); for (Int32 count = 0; count < newItems.Length; count++) { Debug.WriteLine(newItems[count]); } } watch.Stop(); Console.WriteLine("for took {0} ticks", watch.ElapsedTicks); Console.ReadKey(); } } }
Each time I run this test, the for loop runs at 70% of the time of the foreach loop, even with the array copy.
While code coverage by itself is not enough to make me change my coding style, a performance improvement and more accurate code coverage is a good enough reason. | https://www.neovolve.com/2008/07/02/foreach-vs-for/ | CC-MAIN-2018-30 | refinedweb | 511 | 55.64 |
How would I limit match/replacement the leading zeros in e004_n07? However, if either term contains all zeros, then I need to retain one zero in the term (see example below). For the input string, there will always be 3 digits in the first value and 2 digits in the second value.
Example input and output
e004_n07 #e4_n7
e020_n50 #e20_n50
e000_n00 #e0_n0
If you want to only remove zeros after letters, you may use:
([a-zA-Z])0+
Replace with
\1 backreference. See the regex demo.
The
([a-zA-Z]) will capture a letter and
0+ will match 1 or more zeros.
import re s = 'e004_n07' res = re.sub(r'([a-zA-Z])0+', r'\1', s) print(res)
Note that
re.sub will find and replace all non-overlapping matches (will perform a global search and replace). If there is no match, the string will be returned as is, without modifications. So, there is no need using additional
re.match/
re.search.
UDPATE
To keep 1 zero if the numbers only contain zeros, you may use
import re s = ['e004_n07','e000_n00'] res = [re.sub(r'(?<=[a-zA-Z])0+(\d*)', lambda m: m.group(1) if m.group(1) else '0', x) for x in s] print(res)
See the Python demo
Here,
r'(?<=[a-zA-Z])0+(\d*)' regex matches one or more zeros (
0+) that are after an ASCII letter (
(?<=[a-zA-Z])) and then any other digits (0 or more) are captured into Group 1 with
(\d*). Then, in the replacement, we check if Group 1 is empty, and if it is empty, we insert
0 (there are only zeros), else, we insert Group 1 contents (the remaining digits after the first leading zeros). | https://codedump.io/share/ziVS3nGVQPtz/1/python-regular-expression-replacing-a-portion-of-match | CC-MAIN-2016-44 | refinedweb | 288 | 74.29 |
AWS Partner Network (APN) Blog this space and has been working to improve the Kubernetes experience on AWS.
You can observe this innovation and thought leadership in CoreOS Tectonic, an enterprise Kubernetes distribution. Tectonic provides numerous AWS integrations that enable customers to take advantage of many built-in features of the AWS platform, like AWS KMS for key management, Amazon S3 for backing up important data, Auto Scaling, IAM, and more.
One popular AWS feature that has been conspicuously unavailable to Kubernetes until now is the Application Load Balancer. This load balancing option operates at layer 7, enabling features like host, and path-based routing, TLS termination, support for WebSockets, HTTP/2, IPV6, and AWS WAF (web application firewall) features.
In collaboration with Ticketmaster, CoreOS has developed an Ingress controller. This resource can create all necessary AWS resources that will enable customers to use Application Load Balancers to route traffic to different services running on their Kubernetes controller.
Quick Primer on Kubernetes Ingress
Kubernetes provides several ways of exposing your services to the Internet. One way is through a resource type called an Ingress, which is a set of rules and configuration for how traffic will be forwarded to your service. Defining an Ingress resource by itself doesn’t do anything, however, and you’ll need an Ingress controller to actually create resources on behalf of your Ingress. An Ingress controller is an application that listens to the Kubernetes API for the creation of Ingresses, and then creates the necessary resources for exposing your service.
The ALB Ingress Controller is designed to create and manage all the necessary AWS components to expose your Ingress via an Application Load Balancer. This means that when you deploy a service and expose it via an Ingress, the ALB Ingress Controller does the heavy lifting of creating an Application Load Balancer, registering your service with the target group, and creating an Amazon Route 53 Alias record to point to your Application Load Balancer. If you delete your service and its Ingress, the Ingress Controller will clean up all the associated resources. Let’s take a look at how this works.
ALB Ingress Controller Workflow
These creation steps are outlined in the Github repository, but I’ll paraphrase them here to prevent too much context switching.
Source:
When an Ingress creation event from the API server is detected [1], the Ingress controller begins to create the necessary AWS resources. First, it creates the Application Load Balancer [2], and parses configuration for the load balancer from the Ingress YAML definition file. Target groups [3] are also created, one per Kubernetes service that will use the load balancer. At [4], listeners are created, which expose the service on a specific port on the load balancer. Routing rules [5] are configured, which specify the correlation between URL paths and backend target groups. Finally, Route 53 resource records [6] are created to represent the domain for your service.
Deploying Your Own ALB Ingress Controller
Let’s walk through a simple demo to set up our own ALB Ingress controller, spin up a sample backend service, and make sure we can actually hit our service through the load balancer at the route we configure.
First, you’ll need a Kubernetes cluster. For this demo, I’m using my Tectonic cluster, which I spun up using the Tectonic installer:
Tectonic installs with a sensible IAM policy applied to your Kubernetes controller instances, but the ALB Ingress Controller adds new requirements, since it now has to manage Route 53 on your behalf. You can find an example IAM policy here:
Since I was starting from the base Tectonic IAM role, I only needed to add the Route 53 section. My IAM policy now looks like this:
Because all Ingress controllers have a dependency on
default-http-backend, we need to deploy that first.
We can do that quickly with the following:
Next, we can deploy the ALB Ingress Controller. The YAML file for deploying the controller is here:
We need to customize a few environment variables in the configuration before deploying, though, so clone it locally, and in your favorite editor, take a look at the following:
These may be fairly self-explanatory, but in case they aren’t:- Set the region in which you’d like your Application Load Balancer created (this will be the same region as your Kubernetes cluster), set the cluster name to something that makes sense (this will appear in AWS logging), and perhaps consider setting
AWS_DEBUG to “true” in your early experimentation so you can look at pod logs for the controller and watch which AWS API calls are being made.
Once you’ve configured the YAML file for the controller, let’s apply it:
Now you have a living and breathing Ingress controller that is listening to the Kubernetes API and waiting to do your bidding. It is ready to create AWS resources when it detects that the appropriate Ingress resources have been created. Let’s move on and do just that.
Deploying a Demo Service and Ingress
For this demo, we’ll use the 2048 game as our web service. We’ll use the same kubectl apply commands to apply the following resource definition .yaml files.
First we’ll create a namespace for these components to run within:
Next, we’ll create the deployment of our backend service. This will deploy the 2048 game application with five replicas across our cluster.
Using the Tectonic console, I can make sure I have my five replicas running:
Now, let’s create a service, which determines how this particular set of pods should be exposed on their respective hosts. We’ll use the following service file:
Once that’s been deployed, I can again verify the configuration in the Tectonic console:
Next, we’ll specify our Ingress. This is the configuration that triggers the ALB Ingress Controller to create resources on our behalf, so we have to provide some information about how our Application Load Balancer should be set up. Here we need to specify the scheme we want for our load balancer (internal or Internet-facing), which subnets it should live in, the security group that should be applied to it, and the Route 53 subdomain we’d like it to create for us.
After we apply this configuration, the ALB Ingress Controller sets off to work. I can open up the Amazon EC2 console and take a look at the resources created.
Here’s my ALB:
A target group has been created and associated with my Application Load Balancer, and my backend instances have been registered:
A resource record in Route 53 has been created and pointed to my Application Load Balancer:
Next Steps
Thanks for sticking with us this far! Go take a look at the ALB Ingress Controller from CoreOS today, and let us know how we can continue to work together to make your Kubernetes experience on AWS even better.
If you have any questions about this or any other aspect of Tectonic and/or Kubernetes on AWS, come hear me talk alongside CoreOS and Ticketmaster at CoreOS Fest, the Kubernetes and distributed systems conference happening May 31 and June 1 in San Francisco. | https://aws.amazon.com/blogs/apn/coreos-and-ticketmaster-collaborate-to-bring-aws-application-load-balancer-support-to-kubernetes/ | CC-MAIN-2018-26 | refinedweb | 1,202 | 53.55 |
Let us learn how to create Exception messages in OAF. This lesson will take us to show that how to create Exception messages, alert messages, warning messages in OAF pages.
- First, create one page in a project.
- Create the Region and two items.
One Item to enter text so take it as “Message Text Input” and another item is “Submit Button”. Hence we already seen in previous chapters how to create Message Text Input item and Submit Button.
- Create the controller and write the code in the process Form Request, we are going to write the code in process form request because whenever we click on submit button based on the condition, the Message should be displayed.
- Here we are creating one Message Text input item, and three submit buttons each button will display different messages.The below figure shows the page structure Contains :Message Component Layout Region—Under it: Message Text Input Item: Message Layout Item—- under message layout item:Submit Button 1 with prompt : Exception:Submit Button 2 with prompt : Alert:Submit Button 1 with prompt : Warning
Now run the page and just see the output how it looks, the below figure shows the sample output and if we observe there is no gap between Submit Buttons and Message Text Input Item.
Now to create a space between buttons and items we have one item called “spacer”. Create two items under Message Layout and select Item Style as a spacer and in Property Inspector give width as 10.
Click on the spacer item hold it and drag it between the Submit Button items, in Message component Layout region directly we cannot create spacer item, so, therefore, create one message layout hold that item and place between Message Text Input item and Message Layout Item which is created early.
Now under the second message Layout item create one item with Item Style as “spacer” and give height as 10 in Property Inspector.
After creation the page structure looks like the following:
Create the controller under the main region and write the code logic in “process Form Request”.
public void processFormRequest(OAPageContext pageContext, OAWebBean webBean)
{
super.processFormRequest(pageContext, webBean);
if(pageContext.getParameter("item3")!=null)
{
String name=pageContext.getParameter("item6");
throw new OAException(name,OAException.ERROR);
}
if(pageContext.getParameter("item4")!=null)
{
String name=pageContext.getParameter("item6");
throw new OAException(name,OAException.CONFIRMATION);
}
if(pageContext.getParameter("item5")!=null)
{
String name=pageContext.getParameter("item6");
throw new OAException(name,OAException.WARNING);
}
}
In the above code item3, item4, item5 are the id values of the Submit Button items with prompt Exception, Confirm, Warning. Item6 is the id value of Message Text Input item.
The import package is :
import oracle.apps.fnd.framework.OAException;
Run the page and see the output. Give some text in Message Input Text and then click on the button to see the messages displayed on OAF. For example, see the following:
Advantages and Dis-Advantages of OAF
Oracle OSB Training in Chicago
Creating First OAF Page in Project | https://tekslate.com/displaying-exception-messages-based-condition | CC-MAIN-2021-31 | refinedweb | 497 | 55.03 |
In this post, we will go through many of the options for building a React app that will get properly crawled by search engines and social media sites. This isn't totally exhaustive but it focuses on options that are serverless so you don't have to manage a fleet of EC2s or Docker containers.
An often overlooked aspect when you are getting started with building full stack web applications in React is SEO because you have so many other components to build to even get the site working that it is easy to forget about it until the end. The tricky thing is that you can't even tell that it isn't working until you submit your site to Google and then come back a week later after it has crawled your site to see that none of your beautiful meta tags are showing up when you do a google search of your site. The left shows what the Google result shows up as, while the right is what you’d expect based on the dynamic tags that you are setting.
The cause for this is rooted in a common design pattern for starting your site with the
create-react-app generator, so let's go through it. After creating the boilerplate, you can add page titles and meta tags with React Helmet. Here’s what a React Helmet component might look like for a typical static page:
const seo = { title: 'About', description: 'This is an awesome site that you definitely should check out.', url: '', image: '', } }, ]} />
When
seo is pulled from static data, there are no issues- Google will scrape all of it. We run into troubles when
seo relies on fetching data from a server. This is the case if instead of a static about page, we wanted to make a blog page where we pull that data from an api using GraphQL or REST. In that case,
seo would be empty initially and be filled in later after we receive data from the server. Here's what a blog page might look like with React Apollo:
const BlogPage = ({ match }) => { <Query variables={{name: match.params.title}} query={BLOG_QUERY}> {({ data, loading }) => { const blog = _.get(data, 'blog'); if (loading || !blog) return <Loading />; const { seo } = blog; return ( <div> }, ]} /> <div> //Code for the Blog post. </div> </div> ) } </Query> } export default withRouter(BlogPage);
Initially, when the data is loading, the
<BlogPage> will simply return the
<Loading /> component. It's only when the loading is done that we move to the main portion of the code block, so the
<Helmet> component will not be invoked until that point. Ideally, we’d like the Google crawler to wait on the page long enough until the data is loaded, but unfortunately, it is not something that we have control over.
There are a couple of approaches you can take to solve this problem and they all have their tradeoffs. We'll first go over some concepts:
Server-Side Rendering
This is where you have a server that runs your frontend website. When it receives a request for a page, the server will take the first pass at rendering the page before it sends you the HTML, js, and css. Any data that needs to be fetched from an api will be fetched by the frontend server itself and the page will be rendered before anything is delivered to the user's browser. This will ensure that a blog page has all of its title and meta tags rendered before it reaches the user. Since the Google web crawler acts like a user, the page that it receives will be all pre-populated with the correct title and meta tags as well so they will be ingested properly.
Static Site Rendering
This is where every page on your website will be pre-rendered at the time of building your site. This is distinguished from Server Side Rendering because instead of a server actively rendering a page when requested, all the possible site pages are pre-rendered and available without any further building required. This approach works especially well with static hosting solutions such as AWS S3 because an actively running server is not needed.
These are the two main classes of rendering, but there are several solutions for these two approaches:
Next.js
Next.js is a server-side rendering framework for React. It will render pages on the fly as they are requested from a user. There are two modes that it can operate in:
Option 1. Actively running a server.
This will run Next.js on an EC2 instance or possibly as a Docker Container.
Pros:
- Standard way of running Next.js.
Cons:
- Have to pay for an actively running server even if it isn't being used. Looking at \$15/month minimum.
- Need to manage scaling up and down server instances as the demand for your site goes up and down. This is where Docker, Kubernetes and a host of managed services come into play and things get complicated really fast at that point. The pro is that at that point your site is probably successful enough that you could pay a DevOps person to take care of this aspect if it is something you don't want to deal with.
- Not currently AWS Amplify compatible.
Option 2. As a lambda function.
Next.js recently introduced a new mode called
serverless where you can build each individual page as a lambda function that gets hosted either through AWS or using Zeit's now service.
Pros:
- Serverless- you just pay for what you use. Likely will be in the free tier until you have hundreds or thousands of users (depending on usage patterns obviously).
- Scales up and down effortlessly.
Cons:
- Need to watch out for the payload size, can't have too many npm packages loaded.
- Can have a slow initial load time if the site hasn't been visited in a while. These so-called cold starts are based on the complexity of your page and the dependencies you have.
- Each page is an entire copy of your website, so it gets download each time someone navigates around (but gets cached in user's browser after).
- Not currently AWS Amplify compatible.
Gatsby
Gatsby is a static site rendered framework for React. It renders pages during the build time so all possible pages have already been rendered as separate html files and are ready to be downloaded before they are even uploaded to the server. This site is actually rendered using this method!
Pros:
- Blazingly fast: nothing to render so the page load times are super fast. Google PageSpeed Insights is going to love your site because it is so quick.
- Great for SEO- all title and metatags are generated during build time so Google has no trouble reading it.
- AWS Amplify compatible.
Cons:
- Can be bad for dynamic sites where not all possible page combinations are known at build time. An example might be an auction website or something where users are generating content.
- No good way to create all possible pages during build time because the data from an api can change in the future.
- Needs additional finagling to handle both static content and dynamic content because you'll have some api calls happening during build time and others during run time.
Gatsby can render dynamics routes, but since the pages are being generated by the client instead of on a server, they will not be populated with the correct metatags and title. Static content will still, however, load. If you had a site that was a Marketplace, as an example, Google would be able to fetch the tags for the static portions of the site, such as the
home page or
posts page, but it wouldn't be able to get the tags for the individual post page
posts/:id, because its title and tags need data from the server to populate.
Prerender.cloud
This is a service that sits in front of your application and pre-renders the content before it delivers it back to the client or the Google web crawler. I’ve used this service before and it works great- PocketScholar, a science app I previously built uses this technique.
Pros:
- It will pre-render any webpage on demand so it is like Next.js but it will work with an existing create-react-app or statically generated site such as Gatsby or create-react-app's
build staticoption.
- You deploy it yourself using a cloud formation stack on your AWS account.
- AWS Amplify compatible.
- You are serving your site from a static s3 bucket, so it will infinitely scale as you get more users and you only pay for what you use.
Cons:
- It's a service that you pay for based on the number of requests that your web application gets per month. It’s initially free but then is \$9/month for 600-20,000 requests.
- It doesn’t eliminate the cold starts that are present with AWS lambda- it can take a few seconds to load a website if the lambda hasn’t been used in the past 25 minutes or so.
Conclusion
There are a few ways to handle React and SEO and each has its benefits and drawbacks. Here is a table with the highlights:
* A Gatsby dynamic route will not set the metadata or title because it needs to fetch data from the server.
Starting with Create React App (CRA), we can see that while it is serverless which makes it easy for scalability and cost, that it fails for SEO purposes for any content that is dynamic. Prerender.cloud is a good option to put in front of a CRA app because it adds the rendering capability for search engines and social media sharing purposes, but it has the disadvantage of cold starts from the lambda function which can make it a little slow if the site hasn't been accessed in the past 25 minutes.
Gatsby is great for static sites and it wins in the speed department. It will allow you to have dynamic routes, but it won't allow you to benefit from SEO on those routes because it will need to fetch data from the server when rendering those routes on the user's browser.
Next.js is great for both dynamic and static routes but you've previously had to manage a running server instance. A glimmer of the best of all worlds lies in the serverless mode for Next.js. Although slower than Gatsby, pages get rendered on the fly so all relevant tags will be populated with their proper values for web crawlers. The only potential downside with this approach is that Next.js is currently not supported by AWS Amplify, so you can't use it with the automated deployment pipeline, authentication, or App Sync GraphQL endpoint.
There is more where that came from!
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Originally posted at Code Mochi.
Discussion (4)
Hi, great article ! Definetly worth reading.
That's a subject I've been curious about for some time but I never took the time to really get into it. In my peregrinations I've read that there are some ways to generate a sitemap for react apps through some tools like react-router-sitemap and then complete the generated result with the dynamic routes (which we can fetch and build from a database for example). I would be very grateful if you could share your thoughts about that and how you think it compares to the options you present in this article.
I realise that my remark might be a little beside the point since I don't how that would work in a AWS environment. Also it needs some server mechanism to fetch the dynamic content and update the sitemap.
Thank you for any insight you can share.
Thanks for the awesome suggestion! I actually just figured out sitemaps for Gatsby and Create-React-Apps so I'd be happy to create a walkthrough with screenshots and post that up. Out of curiosity, which kind of base boilerplate are you working off of (gatsby, nextjs, create react app)? I want to make sure I at least capture that one so it's helpful. :)
The technological stack I'm thinking about is the one we use at my company which has been satisfying so far. For you to have an idea of our base technological stack and principles I think the easiest way is to share with you one of our sources of inspiration : freecodecamp.org/news/how-to-get-s.... The server side is handled by a web service (ASP.Net Core WebAPI) which serves data stored in a SQL Server database.
We have some apps running with this stack but they are all only used in our customers' intranet. SEO has never been a concern so far. It's definetly going to become a subject at some point however. In our situation, I can surmize that the sitemap would be updated regularly by a planned task in corelation with the data in the database.
I'm not sure if it's relevant to stick with this stack for your walkthrough. I'm not sure how common/standard this stack is. Anyway having a walkthrough on the sitemap usage sor SEO would be amazing !
Thanks for the rundown of your stack Jean-Christophe. That's super interesting that you've coupled Gatsby together with ASP.Net, I haven't seen the blending of C# and javascript like that before. Luckily, from a frontend perspective, it doesn't actually matter what your backend uses as long as you are using Gatsby. I put together a post here that will take you through how to use a sitemap plugin to add generation to your website and then how to submit it to the Google search console. Enjoy and let me know if you have any more questions: codemochi.com/blog/2019-06-19-add-... | https://practicaldev-herokuapp-com.global.ssl.fastly.net/codemochi/a-definitive-guide-to-seo-with-a-serverless-react-application-in-2019-po8 | CC-MAIN-2021-10 | refinedweb | 2,366 | 69.21 |
I often read about novice programmers’ aspirations for a greater density of code comments, because they think it’s “professional”. I have news for you. Professional coders don’t comment their own code much and never trust the comments of others they find in code. Instead, we try to learn to read code and write more readable code.
API Documentation vs. Code Comments
I’m a big believer in clear API documentation. Java makes this easy with javadoc. It even produces relatively spiffy results.
But if you look at the LingPipe source code, you’ll find very few code comments.
The reason to be very suspicious of code comments is that they can lie. The code is what’s executed, so it can’t lie. Sure, it can be obfuscated, but that’s not the same as lying.
I don’t mean little white lies, I mean big lies that’ll mess up your code if you believe them. I mean comments like “verifies the integrity of the object before returning”, when it really doesn’t.
A typical reason for slippage between comments and code is patches to the code that are not accompanied by patches to the comments. (This can happen for API doc, too, if you fiddle with your APIs.)
Another common reason is that the code author didn’t actually understand what the code was doing, so wrote comments that were wrong. If you really mess up along these lines, your code’s likely to be called out on blogs like Coding Horror or Daily WTF.
Most Comments Considered Useless
The worst offenses in the useless category are things that simply repeat what the code says.
// Set x to 3 x = 3;
It’s even better when embedded in a bloated Fortran-like comment block:
/****************************************** ************* add1 *********************** ****************************************** * A function to add 1 to integers * * arguments * * + n, any old integer * *****************************************/ public int add1(int n) { return n+1; }
Thanks. I didn’t know what
int meant or what
n+1 did. This is a classic rookie mistake, because rookies don’t know the language or its libraries, so often what they do seems mysterious to them. For instance, commenting
n >>> 2 with “shift two bits to right and fill in on the left with zeroes” may seem less egregious, but your reader should know that
>>> is the unsigned shift operator (or look it up).
There is a grey line in the sand (I love mixed metaphors) here. When you’re pulling out techniques like those in Bloch and Gafter’s Java Puzzlers, you might want to reconsider how you code something, or adding a wee comment.
Eliminate, don’t Comment Out, Dead Code
I remember being handed a 30-page Tcl/Tk script at Bell Labs back in the 1990s. It ran some kind of speech recognition pipeline, because that’s what I was up to at the time. I picked it up and found dozens of methods with the same name, and lots of commented-out code. This makes it really hard to follow what’s going on, especially if whole blocks get commented out with
/* ... */.
Please don’t do this.
You should lLearn any of thea version control system s instead , like SVN.
When do I Comment Code?
I add comments in code in two situations. The first is when I wrote something inefficiently, but I know a better way to do it. I’ll write something like “use dynamic programming to reduce quadratic to linear”. This is a bad practice, and I wish I could stop myself from doing it. I feel bad writing something inefficient when I know how to do it more efficiently, and I certainly don’t want people reading the code to think I’m clueless.
I know only one compelling reason to leave comments: when you write code that’s not idiomatic in the language it’s written in, or when you do something for efficiency that’s obscure. And even then, keep the comments telegraphic, like “C style strings for efficiency”, “unfolds the E step and M step of EM”, “first step unfolded for boundary checks” or something along those lines.
Update: 13 Dec 2012. I’ve thought about this issue a bit more and wanted to add another reason to comment code: to associate the code with an algorithm. If you’re implementing a relatively complex algorithm, then you’re going to have the algorithm design somewhere and it can be helpful to indicate which parts of the code correspond to which parts of the algorithm. Ideally, though, you’d just write functions with good names to do the stages of the algorithm if they’re clear. But often that’s not really an option because of the shape of the algorithm, mutability of arguments, etc.
Also, I want to be clear that I’m not talking about API comments in code, which I really like. For instance, we do that in LingPipe using Javadoc. I think these comments are really really important, but I think of them somehow more as specifications than as comments.
Write Readable Code Instead
What you should be doing is trying to write code that’s more readable.
I don’t actually mean in Knuth’s literate programming sense; Knuth wants programs to look more like natural language, which is a Very Bad Idea. For one, Knuth has a terrible track record, bringing us TeX, which is a great typesetting language, but impossible to read, and a three-volume set of great algorithms written in some of the most impenetrable, quirky pseudocode you’re ever likely to see.
Instead, I think we need to become literate in the idioms and standard libraries of the programming language we’re using and then write literately in that language.
The biggest shock for me in moving from academia to industry is just how much of other people’s code I have to read. It’s a skill, and I got much better at it with practice. Just like reading English.
Unfortunately, effective programming is as hard, if not harder, than effective essay writing. Writing understandable code that’s also efficient enough and general enough takes lots of revision, and ideally feedback from a good code reviewer.
Not everyone agrees about what’s most readable. Do I call out my member variables from local variables with a prefix? I do, but lots of perfectly reasonable programmers disagree, including the coders for Java itself. Do I use really verbose names for variables in loops? I don’t, but some programmers do. Do I use four-word-long class names, or abbreviations? The former, but it’s another judgment call.
However you code, try to do it consistently. Also, remember that coding standards and macro libraries are not good places to innovate. It takes a while to develop a consistent coding style, but it’s worth the investment.
October 15, 2009 at 7:31 pm |
I find that commenting code is useful when the desired end result is qualitative – UI code, things where you’re trying to rank things according to some fuzzy and ill defined notion of “goodness”, etc. There ends up being a lot of trial and error trying to figure out what works, and the design process isn’t always obvious from the end result: Why we do it this way and not the other, what this magic parameter is for, etc. The rules are relatively ad hoc, and thus no matter how clearly they’re expressed the reason behind them can’t be obvious from the code.
October 16, 2009 at 8:37 am |
Hy David,
Unfortunately you are not quite right. Whe you apply the principles of clean code to your own code and refactor a lot in your TDD process your code is automatically easier to read and understand. The true art in coding lies in writing understandable and readable code which is self explanatory.
When you mention the magic parameter. That’s were the problem lies hidden. If you define meaningful names for your magic parameters and assign it for example with predefined meaningful constants your client of the code must not think a minute why you are passing in these parameters. Because the context and the name defines its purpose.
Daniel
October 19, 2009 at 3:09 pm |
I disagree. It doesn’t matter if you define your parameters: You still need to comment as to why they have that value.
Suppose I want to ignore all objects that have some attribute smaller than a particular value
if (foo.stuff < 3)
ignore(foo);
I can rewrite this to
val StuffThreshold = 3;
if(foo.stuff < StuffThreshold)
ignore(foo);
or
def isBad(foo : Foo) = foo.stuff < StuffThreshold
if(isBad(foo))
ignore(foo);
You could argue that this is more clear. I don't particularly think it is, but I don't care to have that argument. Either way it's certainly not done anything to enlighten us about why the value "3" was chosen, and for good reason: It was derived experimentally.
Your argument presupposes exactly the reason why it is wrong: Not all values have "meaning" other than "this is the value that works". Comments which explain what happens when you twiddle these values and why this particular one has been chosen. Factoring out this supposedly "unclear" code has done nothing except go to great lengths to elucidate the bit that was obvious (what the code was doing) and nothing to explain the process by which it was arrived at.
October 17, 2009 at 7:08 pm |
I do not totally agree with this post, though I believe in writting readable code.
Comments such as “// add 1 to x” is indeed useless (should be punishable IMO). However, writting a small and clear comment for a group of lines of code can be a real time saver for someone who has to go through your code to correct a bug, especially if it’s a language they are not totally familiar with, or with classes they have not yet mastered (e.g. GUI code). The main goal of writting comments should be to give extra details (something that cannot be expressed with clear lines of code, that happens). that also means that you don’t have to write comments in all methods (though the method comment (e.g. javadoc) should be written in most cases).
Comments should also be something a developper does not overlook when writing/updating code. This is a boring task, but not doing it well will end up costing more money that what you saved when you “forgot” to write and/or update them).
October 17, 2009 at 9:49 pm |
I have to disagree even more strongly with your theory. I have never seen code that wouldn’t benefit from better commenting. Occasionally (rarely) that’s fewer or more accurate comments, often its clearer comments but its almost always just ‘more comments’. If you ignore the red herrings of comments that are wrong or say something utterly useless then you have the *usual* case. (In 15 years of programming I’ve seen the /* increase x by 3 */ type of comment dozens of times and every one was in an article about bad comments. I’m pleased to report that few people are that dumb but we all have one or two anecdotes that come close.)
So, why comment in the usual case (which is code that has about 2-4 lines per hundred… my random measure for the sake of this discussion)? Its always clearest to me when I think about what exactly we do that has value. We write lines of code. A line of code is kind of like an atom — its not too useful when you break it apart (sometimes dangerous) and nothing (software, anyway) is built from anything else. A class… is a bunch of lines. A module/library is a bunch of classes. An application is a bunch of modules. And enterprise application is usually stitched together applications (stitched by… lines of code). For sure, you will want to document your applications. Its all a hierarchy of lines of code so the question isn’t “why are comments bad when API docs as javadoc comments are good?”. The question is where in the hierarchy is the best place to *stop* commenting/documenting.
The obvious answer to that question is: “When comments create worse problems than they solve”. Thats an abstract quality that we are all supposed to understand. I don’t understand why we should think that API docs are (even usually) the place where that happens. It almost never is. “…but what about self-documenting code?”. Self-documenting code is like the Axis of Evil. Its a string of weasel words that pre-supposes the correctness of one side of the argument. If code is self-documenting then the comments were written when the code was. Take an example. Say there is one function… 15 or so lines long. You are familiar with the application because you read the docs and got what you could from browsing the API docs. Maybe you even looked at some of the code for a few minutes. You are asked to figure out what one specific function is for (you have had this exact experience before. Its called debugging :-) ). How much time will it take to answer that question (to reasonable certainty… I’m not talking about really digging deep… just searching for why you are ‘getting this crash’). My rule of thumb is this:
Function has a comment (again, not a moronic one but one written by someone who at least tries to write good comments) : scale factor = 1x
“Self-documenting” code: scale factor = 10x +
“Normal” code (which even most proponents of not commenting will admit isn’t exactly self-documenting): scale factor = 100x +
It would never take more than about 2-3 seconds to read the comment or I could probably read and understand the ‘self-documenting’ function in 30-60 seconds. Do that, say, 8 times and then you’ve tracked down the bug. Do that a few times a day for a few months and you will want the original code’s author hanged for sloth.
One last argument I frequently hear against comments is that ‘all comments are wrong’ (by this, I assume people mean ‘most’ comments are wrong). This is probably true but its also missing the point. Most code is wrong. No one suggests you stop writing code. The suggestion is: “Do better”. Thats what comments call for. I’ve also found that many ‘pros’ don’t comment their code. I work with many such pros. Its too bad because they are good engineers whose careers stall because their projects slip or require so much of their time in maintenance while my projects live on for years and do not require so much maintenance (and managers notice…). How is that? Easy. My code isn’t better than theirs but anyone can *fix* or augment my code in a short period of time because its … commented. All the while, other’s tools become more and more of a time sink.
Lastly, the thing I understand least about this debate is that coding is so much easier when you write the comments *first* (CDD?). It goes back to the hierarchy debate but laying out the hierarchy in comments and code ‘framework’ first (function declarations with empty definitions, etc). Are we still fighting the code-planning step of development? If not, I don’t know why this is still such a holy war. I want to know about someone who was burned by a valid comment. The worst I can come up with is that they can be a little ugly (although good comments are compact and cleanly formatted… which usually means unformatted). For every one mentioned, I will post 10 times that a good comment saved my sanity. Feels like a safe bet.
October 18, 2009 at 8:23 am |
Sandman, you are obviously passionate about this topic. Given that my experience is quite different than yours it causes me to wonder why different programmers have such different perspectives on this issue. One possibility is that some developers are better at reading code than others. In other words, some programmers would prefer to read a few sentence natural language description than read a similar number of lines of expressive code (let’s assume expressive code written by good programmers just as you assumed good comments). For myself, I make an effort to write code that both humans and computers can understand. Again assuming the humans can read code. I prefer that approach since it eliminates duplication and the extra effort and risk of errors associated with it. Also, my experience is that most programmers don’t know when to write appropriate comments (in other words, your assumption is not typically true in my experience) and instead they comment many things that don’t need comments and over time the comments diverge from the implementation. Both lead to wastes of time which I imagine are comparable to your own imaginary time multipliers attributed to uncommented code. You want to know someone who’s been burned by a valid comment. I’m certainly not one, but I’ve been burned by useless and bad comments (I know you didn’t ask that question). I seldom pay much attention to comments when debugging code and I’m known to be quite good at debugging software problems. In fact, it’s not uncommon for me to help someone debug their software over the phone with no access to the code at all.
I also wonder if there might be some aspect of this debate that is related to open source software. During my several decade career as a programmer I often learn how software works by reading source code. Maybe people that do that frequently become better at reading code, see more instances of invalid comments, and therefore value expressive code over (bad) comments. On the other hand, I also value valid, useful comments that are not just duplicating what’s clear in the code. To play the devil’s advocate, I do understand why people that must work with non-expressive code would prefer more heavily commented code. Given that you appear convinced that self-describing, expressive code is very rare or even possible then I understand your position. However, I believe the premise is incorrect based on my experience.
October 19, 2009 at 6:55 am |
@Frank Smith
Is this a case of “If you don’t like the argument, attack the source”? It seems to me that though Sandman’s comment is a reasoned argument, your response is simple “I’m better than you”. If your argument is that some developers can’t read code as well as a genius such as yourself, you’d better comment your code so that they will be able to maintain it.
October 19, 2009 at 9:42 am |
I’m surprised you think I’m attacking the source. I attacked some of the “statistics” drawn from thin air, but I assume Sandman is a good, solid programmer. I did explore some of the possible reasons why the perspective he described exists when there are many who believe quite differently. The ability to read code is one reason and, yes, I believe code reading ability is one skill, among many, that is important for a good programmer. Fortunately, I work with developers who tend to have that skill (it’s certiainly not my personal genius) and good code writing skills so commenting is not as necessary as some people might believe. As you said, if I worked with programmers who generally did not have skill I’d tend to comment more (and look for other employment).
October 19, 2009 at 1:34 pm |
I had to rant about this one so much I started a blog and posted my reply there.
October 19, 2009 at 2:39 pm |
Speaking of futility, that link’s broken and the blog doesn’t exist. Maybe a permissions problem?
October 19, 2009 at 2:36 pm |
I added some examples in this followup, Examples of “Futility of Commenting Code”.
October 19, 2009 at 2:43 pm |
Interesting I just visited the blog 30 minutes ago and it was there…
Here is the comment he made on the blog:
I fired up the RSS reader this morning and spotted a real gem, “The Futility of Commenting Code”. By “gem”, I mean a piece of dirt that has been buried for a damn long time. OK, it hasn’t been buried yet but it should be.
Every month or two, if you subscribe to DZone feeds, you will see a blog post or article that explains why you shouldn’t comment your code. This post was one of them but they all need to be refuted. My irritation at this recurring theme has led me to be a refuter via this blog. I could have commented on the OP but I reckon this rant may last a while.
Let’s take it from the top…
Professional coders don’t comment their own code much and never trust the comments of others they find in code. Instead, we try to learn to read code and write more readable code.
I never get the read-the-code argument. Code that others wrote, and probably code you wrote yourself twelve months ago, can be hard to read. Other people have different styles to you. I like short, well-named methods. It means that what some developers might code in a twenty line method I may put into four five liners or five four-liners. Now, when Mr Maintenance-Programmer looks at my code I hope he finds it easy to read and specifically, to understand the intent. However, he didn’t spend months working with ABC plc and doesn’t understand the inner workings of project accounting so maybe he doesn’t get it. He could spend five mintes reading the code (or perhaps a lot longer in a large codebase), following the possible flow of control of multiple methods and struggling with the rule of seven. He could also read a one-line succinct comment and realise that that this isn’t the code he is looking for.
The reason to be very suspicious of code comments is that they can lie. The code is what’s executed, so it can’t lie.
Wanna bet? I’ve seen plenty of code that isn’t maintained properly that lies. Sometimes when the pressure is on and potential lawsuits are building, management insist on quick fixes. That often means that that wonderfully-named method now does something that really belongs elsewhere. Of course, when you are doing quick-and-dirty fixes you could edit a hundred methods. When you come back and refactor ninety-eight of them you are left with method names that lie. Yes comments can lie too, but only if you treat them as second-class citizens. Maintain your code, maintain your comments. Problem solved.
Another common reason is that the code author didn’t actually understand what the code was doing, so wrote comments that were wrong.
Maybe if you had commented that code he wouldn’t have had to read and misunderstand it.
The worst offenses in the useless category are things that simply repeat what the code says.
Ah yes, good old // Set i to 3. Personally I have never seen such an inane comment in production code. If I did, I would remove it and talk with the developer who put it there in the first place (unless he has resigned and gone off to pursue his gardening passion). This is a straw man argument, not a sensible one. Comments are suppose to tell you the intent of the programmer – something often not present and maybe impossible to express in the code. Or maybe to tell you why that apparently inefficient code is good because it avoids a framework bug (and which version of the framework because maybe it’s been fixed now).
Eliminate, don’t Comment Out, Dead Code
Good point, though sometimes leaving the dead (or maybe still twitching) code in there can be useful. At least until you have the new code living breathing and tested to within an inch of its life. Then stamp on the old stuff and hit Del before your next check-in.
This all feels a little bit like the wrong type of laziness. Some laziness is good. It’s the reason we have cars, planes, ships and bad air quality. OK, perhaps the air quality argument is a tricky one to win. Bad laziness means that software isn’t documented, there isn’t a help file, the code isn’t well-structured and is hard to read and uncommented. You just need to treat comments as a part of the source code and ensure you update them. If, like me, you have short methods, it’s not even as if the comments are off the screen so get missed.
So why did I write all this?
Some programmers are very vocal in their expression that comments are bad and shouldn’t exist at all. They probably really mean that most comments are a waste but some are good. Even the author of the OP mentions that he does comment occasionally. Bad comments are as bad as bad code. Good comments improve the code and increase efficiency. This topic is not, at some would reason, black and white.
October 19, 2009 at 2:57 pm |
@Daniel Marbach: Thanks for the repost.
I didnt’ realize this was a recurring theme on developer blogs, but I wouldn’t be surprised.
Just to be clear, I didn’t mean to imply that method names can’t lie. I meant the code itself can’t lie. You have to be just as suspicious of method names as comments.
Also, I’m all in favor of documenting intent. I’m pretty sure we’d all agree that the main intent of a package, class or method should be documented in the API.
So what about really tricky bits of code that aren’t clear (and either can’t be refactored due to efficiency/modularity, or aren’t worth refactoring)? By all means, comment away.
I didn’t mean to imply that code shouldn’t be commented at all! Maybe it was the marketing department’s provocative title?
I actually think the code that Sun distributes with the JDK for most of the public classes in Java is a good example. You’ll find very few comments in there. Now having said that, I’m actually seeing many more in java.util.ArrayList than I remember seeing anywhere else. Ditto for java.lang.String. Many more than I’d likely use, but nothing of the silly or completely useless variety. On the other hand, java.lang.Math has all sorts of comments on delegation that fall into what I’d consider the totally useless category:
October 19, 2009 at 6:56 pm |
[…] something called The LingPipe Blog comes the futility of writing comments. It’s an old, oft-repeated-but-hardly-followed rule: comments are a code smell. But like all […]
October 27, 2009 at 6:10 pm |
I routinely write multi-paragraph comment blocks (>100 lines) to explain the math behind some intricate C code (talking about scientific/numerical code). These would typically appear at the head of a function implementing the idea. Then the within-code comments can be kept to a manageable level.
I’ve never had second thoughts about this. As I’ve spent more time programming, these comment blocks have become more typical of code I write.
For the easy stuff, I agree, better to restrict to API comments, gotchas, loop invariants — key bits.
October 28, 2009 at 1:36 am |
[…] Shared The Futility of Commenting Code « LingPipe Blog. […]
November 22, 2009 at 11:10 pm |
Real programmers don’t comment their code. If it was hard to write, it should be hard to understand :-)
May 21, 2011 at 9:45 pm |
Hog Wash!
We don’t live in a perfect world where everything is immediately clear; we don’t live in a perfect world where every programmer on a team actually cares or has the ability to write crystal clear code; we don’t live in a perfect world where every bit of code we write will be so clear that it documents itself. We don’t have perfect memories that never forget what we were doing the day before or why we chose a certain method of doing something over another. Comments help with this!
The that gets me is that the people saying ‘no comments’ haven’t done any real research into the topic. For example, what state is your mind in when reading code (i.e. variable names and unit test)? What state is your mind in when reading natural language? Which do you comprehend more easily? I know that when I read code my mind isn’t in the same state as when I read natural language prose. Also, research (REAL LIVE RESEARCH — novel isn’t it) indicates that programmers are pretty good at updating comments when code changes.
Could we stop propagating this lie please?
May 23, 2011 at 11:25 am |
If you go back and read what I wrote, you’ll see that I don’t say “no comments”. I specifically think API comments are critical for both inter-developer communication and the eventual clients. I also list a couple reasons why I think comments in code can be useful.
Judging from the abstract of the paper you link (the content’s paywalled), they seem to include API and method comments as well as the in-code comments I was specifically trying to address.
I’m speaking from experience, not hearsay or myth propagation, when I say that comments get stale in almost every piece of code I see. For instance, another message that arrived in my e-mail today is about the API drift and stale comments in the API doc for the C++ Matrix library Eigen. Last week, I sent the Eigen developers comments about stale abstract base class doc in an obscure corner of their API. I’m not picking on Eigen, which is a great lib and very well documented and testedl. The point is that I had to dig into the code to see how to extend a virtual class properly to act as a template arg. | https://lingpipe-blog.com/2009/10/15/the-futility-of-commenting-code/ | CC-MAIN-2021-31 | refinedweb | 5,117 | 71.04 |
Using PHP with FormsOnce you know the basics of PHP's syntax and structure, it is fairly easy to make the leap to writing full-fledged scripts.
Because working with forms is one the most common tasks in writing applications for the web, the first script we write will be a form processor. Though a fairly mundane application, it will introduce you to a range of important concepts, including how PHP handles variables that come from outside the running script.
First, let's take a quick look at the HTML end of forms, and go into a little bit of detail about how data is passed from forms to the server.
Form Basics
You have probably worked with HTML forms dozens of times, but have you ever really thought about how they work?
Take a look at the following:
This is probably one of the simplest forms you could have in a page. It contains a text field called "name" and a submit button. Notice the method specified in the opening form tag.
As you might remember, there are two options for the method -- GET and POST -- which determine how information is passed from the form.
Without getting technical, here's the difference: GET sends the form information appended to the URL which is the same way that information is sent from a link. POST, on the other hand, sends the information transparently as part of the header of the page request.
Unlike GET, information sent via POST is not affected by any browser limitations on the length of URLs, and is not visible to the user. It is for this reason that POST is usually the chosen method for forms, unless you are debugging your script and need to see what is being passed to it. You will see why this distinction is also important to remember for the purposes of programming a little later on.
From the Form to PHP
Once a server receives information from a form posted to a PHP script, the programming takes over. This is where PHP really starts to shine. Every value passed from the form is automatically available to the script using the name given to the input in the form. For example, if you used the sample form above, and entered "Billy Joe Bob" for the name, then the name of that value in the script would be accessed as a variation of "name".
The version of PHP running and configuration of the php.ini file determines exactly what variation the value will be available by. These settings affect forms and data passed via links as well as predefined server and environment variables. Here are the possible situations:
- track_vars setting is on in the php.ini file: GET, and POST variables (among others) will be available through global arrays: $HTTP_POST_VARS and $HTTP_GET_VARS. For example: $HTTP_POST_VARS["name"]. Note: these arrays are not global.
- register_globals setting is on in the php.ini: GET and POST variables will be available in the format of standard variables. For example: $name. Variables passed from forms are automatically part of the global namespace.
- register_globals and track_vars are on in the php.ini: variables are available in both forms.
- PHP version 4.1.0 and higher: Due to security concerns, register_globals is being deprecated. Though still on in default configurations of 4.1.0, following releases will not have the setting enabled. New, shorter, arrays have been introduced to replace the old $HTTP_POST_* arrays: $_GET, $_POST. These arrays are also automatically global. For Example: $_POST['name']
Writing a Form Mailer
Before you write any script, it is important to analyze what functions you need to perform and come up with a brief outline. For this script, there are a couple of things we want to include beyond simply sending the contents of the form: - Display a form and allow the user to submit their name, email and a message. - Make sure all required fields are filled in. - Display a message and redisplay the form if required fields are missing. - Do some simple validation on the users email address. - Send the user's message via email - Display a thank you page. Just like any other project, having a mental or written blueprint of what you want to do cuts down on the amount of changes because you forgot something and makes writing the script easier and faster.
The Form
Save this as form.php and take a look at it. For the most part, this form is strictly HTML. There are 3 input fields: name, email and message that the user will fill out.
Since the scripting that handles the form input will be in the same file as the form itself, we use $_SERVER['PHP_SELF'], a server variable representing the file name of the script that is currently running, as the form action. Essentially, we are posting the form back to the current URL, whatever that may be.
<?=$errormessage?> does not output anything unless there is an error in the user input - in which case its replaced by the error message.
Also notice that PHP is used to set a default value for each of these fields. If the user leaves one of the required fields blank, we will want to redisplay the form. To keep them from needing to re-type information, we use the values from the first time they submitted the form to pre-fill the fields.
The hidden field contains a comma delimited list of the field names we want to be required; it will be used to cycle through all of the values to check to see if they are filled in once the form is submitted.
The PHP
As mentioned before, the PHP to process the form will be in the same file as the HTML. This makes it easy to redisplay the form should there be an error in what the user submitted. So that the PHP is parsed immediately after the form is submitted, it should appear in the file before the HTML. If the form is validated, we will send the email and stop the execution of the script before the form is reached again. If there is a problem with what the user submitted, we will assign an error message to $errormessage and the form will automatically be displayed, since it comes after the PHP.
The first line of PHP needs to check to see whether or not the form has been submitted. The easiest way to do this is to see whether a value from the form is present or not. Since the value of the submit button is always passed with the form, it is idea to use for checking:
Add this code snippet before the html for the form in form.php, and run the file from your browser. When you fill out the form and press submit, you will see "the form has been submitted" at the top of your browser, followed by the form. Putting all the code to validate and send the contents of the form within this if statement will ensure it will only execute if the form has been submitted.
The next step is to check and make sure that all of the required fields are filled out. To do this, we need to grab the list of required fields from the hidden form field and split them into an array. Once they are in array form, we can loop through them checking to make sure the associated variables are not empty.
To split the list, we can use one of PHPs built in functions, explode(), which "explodes" a string on the occurrence of another string, and assigns the results to an array:
Now that we have an array that contains the required fields, we can loop through it. If a field does not have a value, we need to indicate that it's missing. The easiest way to do that is by incrementing a counter each time a variable is empty:
Here the execution of the script branches.
If $error is still equal to 0 after the end of the loop then we know that the user filled in all the fields and we can go on to do some simple validation of the email address:
Using the built in PHP function, strstr(), this if statement simply checks to make sure there is a @ and period in the email address. Though you can perform more complex validation that checks for the proper syntax of email addresses, and even checks to make sure the entered domain name is valid, this will weed out the more creative fake addresses a user might enter.
If the email address contains both of these values, then we can send the users email.
PHP includes a function to send email called mail(). It follows the following format: mail (TO, SUBJECT, MESSAGE (optionally:, additional headers, paremeters).
Optional additional headers includes information such as the From and Reply To addresses, any additional recipients and the content type (for sending email as plain text or html) to name a few. For this script, though, all we need are the basic parameters (remember to replace "youremail@your.com with your own email address):
After sending the email, we need to display a message to the user letting them know that their email has been sent. Since they submitted their name, we can use it to personalize the message:
Or even better, redirect them to another page:
Since we passed the name appended to the URL in the second sample, you could also use it in thanks.php in the form of $_GET['name'] (remember, variables passed via urls are available in the $_GET array). Including the exit statement after the print or header statement ends the execution of the script; it is used here so the form is not redisplayed.
Now that we have handled the part of the script that sends the email, we need to work more on the error handling. We bundled the code block for validating the email within an if statement checking to make sure all the fields, and the code block for sending the email within the if statement validating the email. To display a message if there are errors in the form, we need to work backwards logically.
First, the if statement for the email validation is closed, and an else statement is defined to display a message should the email not validate:
Finally, the if statement for the field checking is closed and an else statement is added to specific what should happen if any fields are empty, the opening loop to see if the form was submitted is also closed:
Thats all there is to it. You can view the whole script here, or save your working file and test the form in your browser.
Finally
You can easily expand on this form for all different sorts of applications. Next time, we will explore how to work with files, and revisit forms to create scripts that store and update information on the server.<< | http://www.developer.com/lang/php/article.php/996351 | CC-MAIN-2017-39 | refinedweb | 1,843 | 67.89 |
I've written a function to remove certain words and characters for a string. The string in question is read into the program using a file. The program works fine except when a file, anywhere, contains the following anywhere in the body of the file.
Security Update for Secure Boot (3177404).
def scrub(file_name):
try:
file = open(file_name,"r")
unscrubbed_string = file.read()
file.close()
cms = open("common_misspellings.csv","r")
for line in cms:
replacement = line.strip('\n').split(',')
while replacement[0] in unscrubbed_string:
unscrubbed_string = unscrubbed_string.replace(replacement[0],replacement[1])
cms.close()
special_chars = ['.',',',';',"'","\""]
for char in special_chars:
while char in unscrubbed_string:
unscrubbed_string = unscrubbed_string.replace(char,"")
unscrubbed_list = unscrubbed_string.split()
noise = open("noise.txt","r")
noise_list = []
for word in noise:
noise_list.append(word.strip('\n'))
noise.close()
for noise in noise_list:
while noise in unscrubbed_list:
unscrubbed_list.remove(noise)
return unscrubbed_list
except:
print("""[*] File not found.""")
Your code may be hanging because your
.replace() call is in a
while loop. If, for any particular line of your
.csv file, the
replacement[0] string is a substring of its corresponding
replacement[1], and if either of them appears in your critical text, then the
while loop will never finish. In fact, you don't need the
while loop at all—a single
.replace() call will replace all occurrences.
But that's only one example of the problems you'll encounter with your current approach of using a blanket
unscrubbed_string.replace(...) You'll either need to use regular expression substitution (from the
re) module, or break your string down into words yourself and work word-by-word instead. Why? Well, here's a simple example:
'Teh' needs to be corrected to
'The'—but what if the document contains a reference to
'Tehran'? Your "Secure Boot" text will contain an example analogous to this.
If you go the regular-expression route, the symbol
\b solves this by matching word boundaries of any kind (start or end of string, spaces, punctuation). Here's a simplified example:
import re replacements = { 'Teh':'The', } unscrubbed = 'Teh capital of Iran is Tehran. Teh capital of France is Paris.' better = unscrubbed naive = unscrubbed for target, replacement in replacements.items(): naive = naive.replace(target, replacement) pattern = r'\b' + target + r'\b' better = re.sub(pattern, replacement, better) print(unscrubbed) print(naive) print(better)
Output, with mistakes emphasized:
Teh capital of Iran is Tehran. Teh capital of France is Paris. (
unscrubbed)
The capital of Iran is Theran. The capital of France is Paris. (
naive)
The capital of Iran is Tehran. The capital of France is Paris. (
better) | https://codedump.io/share/3AJJ61qpUfZ6/1/python-cannot-read-a-file-which-contains-a-specific-string | CC-MAIN-2017-39 | refinedweb | 423 | 61.12 |
Eclipse Community Forums - RDF feed Eclipse Community Forums API Tools - No warnings/errors when changing API <![CDATA[Hello together, I have a problem with the PDE API Tools and Eclipse 3.5 (as well as 3.4). I wanted to use API Tools to check for changes of the API in our RCP application but there is no error output in the problem view. I have done the following things: 1. Converted all plugins for using them with API Tools 2. Set the plugins directory of the previous version as baseline (The plugins in this directory are also configured for using them with API Tools) 3. Now I changed the signature of an API method in my current workspace (public method in public class in an exported package) -> No error or warning appears (Although I set that in the API error & warning preference page) What have I done wrong? Another problem I had, was that eclipse 3.5 noticed that the bundle versions needed to be increased but eclipse 3.4 didn't... Best regards, Philip Corlatan]]> Philip Corlatan 2010-01-17T23:11:33-00:00 | https://www.eclipse.org/forums/feed.php?mode=m&th=160829&basic=1 | CC-MAIN-2021-31 | refinedweb | 186 | 72.46 |
Quoting Oren Laadan (orenl@cs.columbia.edu):> Now we can do "external" checkpoint, i.e. act on another task.> > sys_checkpoint() now looks up the target pid (in our namespace) and> checkpoints that corresponding task. That task should be the root of> a container.> > sys_restart() remains the same, as the restart is always done in the> context of the restarting task.> > Signed-off-by: Oren Laadan <orenl@cs.columbia.edu>(Have looked this up and down, and it looks good, so while it's theeasiest piece of code to blame for the BUG() I'm getting, it doesn'tseem possible that it is)Acked-by: Serge Hallyn <serue@us.ibm.com>thanks, Oren.-serge | http://lkml.org/lkml/2008/10/31/145 | CC-MAIN-2014-35 | refinedweb | 113 | 76.62 |
Aslam o alaikum,
bhai engine overhaul karwana hay to kabhi bhi Gulberg FB area wale Abdul Qadir ke pass mat jana, Alladin wale Raees Papu ke pass chale jao, nahin to best option is Karim Baloch, Holy Family Hospital MA Jinnah Road par.
best of luck with you engine overhaul
Shukria for detailed response.
Waisay qeemat parh ker tou hamari hawa nikal gai hai, good bye to HID!!!!!:-#
@asad and all :<?xml:namespace prefix = o<o:p></o:p> <o:p></o:p>Yesterday i talked to the denter and painter (my trusted ones) to finalize the deal:<o:p></o:p> <o:p></o:p>work is :<o:p></o:p>1. complete bonut scratch (inner and outside).<o:p></o:p>2. Complete roof sctratch.<o:p></o:p>3. complete diggi scratch. (outside only).<o:p></o:p>4. piece rapair on front lower right side.<o:p></o:p>5. piece rapair on rear left side.<o:p></o:p>6. some other minor dentings.<o:p></o:p>7. paint on golas of all doors.<o:p></o:p>8. bumper black paint.<o:p></o:p>9. spray on entire body.<o:p></o:p> <o:p></o:p>Total cost is 10,500/-.<o:p></o:p>colour is metallic blue. <o:p></o:p> <o:p></o:p>What do you say about cost ????<o:p></o:p><o:p> </o:p>
@all:<?xml:namespace prefix = o<o:p></o:p> <o:p></o:p>any suitable polish for daewoo dashboard as its black in colour. i have used imported polish being used for plastics but its result is not that good? any opinion??<o:p></o:p> <o:p></o:p>Unique feature of its dashboard is that its made of gatta with ragazine at top, so how to revitalize the ragazine. <o:p></o:p> <o:p></o:p>yaa phir mochi say polish karwa loon!!!!!!!!!!!<o:p></o:p>
@shah7310500/- is v.v reasonable coz same work could also be done in 15000-20000 budget. but there might be work quality difference as well as paint quality difference. if your painter uses paint of good quality than your deal will be great. i never use any polish on dashboard so can't share any experience .
I have seen many cars painted by him, and quality of work is evry good. I hope smae for me. He uses nippon paint, however i will also check it.
Your car pics have also pushed me ahead to do it at earliest, otherwise i was lingering behind for many months. Task will start from this Friday.
no doubt he would be a good painter and already has done many excellent paint jobs for others , but he must be demanded a different amounts from them as compared to estimate given to you. if he has good relations with u than definately he will do honest job for you otherwise kaam men kuch dandi bhi maar sakta hai. any way best of luck from my side and we will wait for your ride's new looks on pakwheels.
same hereye ameero ke shoq hain bhai, mein apni battian thek kara lnga
@asad
btw which brand paint your painter has used for your car???
pata nahi yaar men nay to usay filhal 6000/- diye hain men dobara us kay paas gaya nahi takay aur paisay denay na paren
Wah bhai Wah, i will try to get some traiing form you for this!!
Aapp nay painter ko paint (thuk) laga di hai!!!!!!!
isi 6000/- men us nay new DAEWOO and RACER ky chorom type Markay bhi trunk par laga kar diye hehheheh , us kay baad say men ghaib howa wa hon agar bohot zid ki us nay to 1000/- aur day donga
Now its time to get out of office after a long farigh day!!!see u tomorrow as usual (not casual)!!
Damn! Damn! never give ya Daewoo even to ya dad..Today unfortunatly gived ma car's key to a frnd. And what he did pulled of ma cars gear lever ( coz reverse hopes at unusual place ) .. am worried k ab kia ho ga?( cos dont know uss na aur kia rang dikhay hon ga ) how much it will cost? and will ma gear get back to its orig cond.. coz it was performing v v well. as ma car is just 45k driven
Thanks bro for suggestion, Kiya aap ne bhi apni ride ka engine overhaul kerwaya hai? ager kerwaya hai tu kaha se or kittnay main ?Thanks
ya Daewoo shouldnt be given to any driver who never dealt with daewoo before. u can get re-adjusted ur gear lever from a good mechanic.
yeh bro will bring the mech today... As there is only best daewoos mechanic is "khair Ullah".. in peshawar.. hopefully nothing else will be wrong.
Haha very interesting, did u asked ur friend keh uss nay gear laganay ki koshish ki thi ya bahar nikalnay ki.DOnt worry, i think it will be refixed in the gera lever bush bush or at max you will need to replace the white bush of the gear lever and it will be fine.
he was saying k ma reverse laga raha tha and gear hath ma aa gaya.. yar meri corolla 07 ka engine seize ho jay koi parwa nahi but meri daewoo pa zara sa scratch bhi par jay neend nahee ati.
i went to mian khan (rwp) to adjust the timing ov ma car.. woh mugha jana he nahee da raha tha.. was sayin u have to sell it to me.. and he said " asi daewoo to korea ma bhi nahee ho gi " mashAllah..
Dont know why am that much in love with her.
yaar mian khan kay paas daewoo kay customer aatay rehtay hain , woh kai dafa mujhy bhi keh chuka hai key daewoo sale to nahi karni. | https://www.pakwheels.com/forums/t/daewoo-fan-club/33414?page=159 | CC-MAIN-2017-09 | refinedweb | 987 | 83.15 |
David Crossley wrote:
>
>.
David, it is by leaving little itches for people to scratch that I
managed to make a good open development community. The first project I
started, JMeter, came up all polished and finished so people used it a
lot, but never had the itch to dive into it and understand it.
Result: no help from the development side and lots of wishes on the user
side. Means: if I left the effort, it would have died.
Fast forward to Cocoon 1.0: it's was a very simple and ugly servlet that
connected XML4j (what became Xerces) and LotusXSL (what became Xalan).
Others would have called it 0.01a, I called it 1.0 and people started to
use it... but there we lots of problems, lots of things to improve...
and now Cocoon is one of the most complex java software in the whole
world.
And this is so *exactly* because I rely on the mindset of developers who
simply can't stand imperfections. So I live them in, on purpose, so that
others are bugged by them, but not enough to turn away, but enough to
jump in, help and get a taste of the underlying ideas.
Doing this for avalon was the biggest difficulty, that's why I moved
away from it and helped James and Cocoon move to Avalon: it's by
patching Cocoon that people get to appreciate avalon. That's how I got
Berin and Peter in.
If Cocoon was perfect, you would have used it and you wouldn't now be
part of the community, you wouldn't have the chance to shape its future,
you wouldn't have the fun and you wouldn't have learned those things
that you learned from us.
All because I relied on the validation pickyness of somebody. And you
happened to be the one to jump in.
Those imperfections that I don't care about are 'ego traps' and I leave
them around because I'm a person hunter: I don't care about good
software, I care about good people and having them in my team.
Those 'ego traps' are the way I do recruiting for open development
communities.
And, like it or not, all of you jumped (probably Sam is the only one who
didn't) in those traps with both feet :)
> > I know, I know, call me captain lazy butt :)
>
> Well i will kick it now and then :-) Sorry, i know that we are
> all busy and some fundamental things get overlooked.
'fundamental' is a highly relative concept, David. For Apache, what I
consider 'fundamental' is having great people in a development
community. Everything else doesn't really matter.
> Perhaps that is my role in life. It seems that everywhere i go
> in XML-land, people are over-looking fundamental infrastructure
> issues, which leads to serious problems down the track. I see
> people publishing DTDs that they have not actually used, and
> i get horrified.
:)
I get horrified for very different things, believe me, but it's because
that we work together than we are powerful. And this is what I care
about most.
> I am not having a shot at you Stefano - just a general gripe.
Oh, please, my patented abstesto underwear has resisted much higher
temperatures :) This is a breeze for me.
> On the cocoon-dev list i am having trouble getting people to
> consider validation issues.
You do? from where I stand, I think you did a great job and people are
(admittedly slowly) listening. It might be that the problems are the DTD
technology which is not powerful enough in a heavily namespaced world
like Cocoon. Have you ever considered switching over to RelaxNG?
Should we for Forrest?
> Anyway, i think that it is important to get these issues sorted
> out early in the life of Forrest.
Absolutely.
> > > There are some issues with Forrest, but i have sorted
> > > most of them out and attach a collection of patches
> > > forrest-patch.tar.gz ...
> > >
> | http://mail-archives.apache.org/mod_mbox/forrest-dev/200202.mbox/raw/%3C3C652100.4F440790@apache.org%3E/ | CC-MAIN-2017-26 | refinedweb | 666 | 71.65 |
This is the first of a series of articles on “Type Parameters and Type Members”.
Type members like
Member
class Blah { type Member }
and parameters like
Param
class Blah2[Param]
have more similarities than differences. The choice of which to use for a given situation is usually a matter of convenience. In brief, a rule of thumb: a type parameter is usually more convenient and harder to screw up, but if you intend to use it existentially in most cases, changing it to a member is probably better.
Here, and in later posts, we will discuss what on earth that means, among other things. In this series of articles on Type Parameters and Type Members, I want to tackle a variety of Scala types that look very different, but are really talking about the same thing, or almost.
To illustrate, let’s see two versions of the functional list. Typically, it isn’t used existentially, so the usual choice of parameter over member fits our rule of thumb above. It’s instructive anyway, so let’s see it.
sealed abstract class PList[T] final case class PNil[T]() extends PList[T] final case class PCons[T](head: T, tail: PList[T]) extends PList[T] sealed abstract class MList {self => type T def uncons: Option[MCons {type T = self.T}] } sealed abstract class MNil extends MList { def uncons = None } sealed abstract class MCons extends MList {self => val head: T val tail: MList {type T = self.T} def uncons = Some(self: MCons {type T = self.T}) }
We’re not quite done; we’re missing a way to make
MNils and
MConses, which
PNil and
PCons have already provided
for themselves, by virtue of being
case classes. But it’s already
pretty clear that a type parameter is a more straightforward way to
define this particular data type.
The instance creation takes just a bit more scaffolding for our examples:
def MNil[T0](): MNil {type T = T0} = new MNil { type T = T0 } def MCons[T0](hd: T0, tl: MList {type T = T0}) : MCons {type T = T0} = new MCons { type T = T0 val head = hd val tail = tl }
{type T = ...}?
After all, isn’t the virtue of type members that we don’t have to pass the type around everywhere?
Let’s see what happens when we attempt to apply that theory. Suppose
we remove only one of the
refinements
above, as these
{...} rainclouds at the type level are called.
Let’s remove the one in
val tail, so
class MCons looks like this:
sealed abstract class MCons extends MList {self => val head: T val tail: MList }
Now let us put a couple members into the list, and add them together.
scala> val nums = MCons(2, MCons(3, MNil())): MCons{type T = Int} nums: tmtp.MCons{type T = Int} = tmtp.MList$$anon$2@3c649f69 scala> nums.head res1: nums.T = 2 scala> res1 + res1 res2: Int = 4 scala> nums.tail.uncons.map(_.head) res3: Option[nums.tail.T] = Some(3) scala> res3.map(_ - res2) <console>:21: error: value - is not a member of nums.tail.T res3.map(_ - res2) ^
When we took the refinement off of
tail, we eliminated any evidence
about what its
type T might be. We only know that it must be some
type. That’s what existential means.
In terms of type parameters,
MList is like
PList[_], and
MList
{type T = Int} is like
PList[Int]. For the former, we say that
the member, or parameter, is existential.
Despite the limitation implied by the error above, there are useful functions that can be written on the existential version. Here’s one of the simplest:
def mlength(xs: MList): Int = xs.uncons match { case None => 0 case Some(c) => 1 + mlength(c.tail) }
For the type parameter equivalent, the parameter on the argument is usually carried out or lifted to the function, like so:
def plengthT[T](xs: PList[T]): Int = xs match { case PNil() => 0 case PCons(_, t) => 1 + plengthT(t) }
By the conversion rules above, though, we should be able to write an
existential equivalent of
mlength for
PList, and indeed we can:
def plengthE(xs: PList[_]): Int = xs match { case PNil() => 0 case PCons(_, t) => 1 + plengthE(t) }
There’s another simple rule we can follow when determining whether we can rewrite in an existential manner.
we should always, ideally, be able to write the function in an existential manner. (We will discuss why it’s only “ideally” in the next article.)
You can demonstrate this to yourself by having the parameterized
variant (e.g.
plengthT) call the existential variant
(e.g.
plengthE), and, voilà, it compiles, so it must be right.
This hints at what is usually, though not always, an advantage for type parameters: you have to ask for an existential, rather than silently getting one just because you forgot a refinement. We will discuss what happens when you forget one in a later post.
Scala is large enough that very few understand all of it. Moreover, there are many aspects of it that are poorly understood in general.
So why focus on how different features are similar? When we understand one area of Scala well, but another one poorly, we can form sensible ideas about the latter by drawing analogies with the former. This is how we solve problems with computers in general: we create an informal model in our heads, which we translate to a mathematical statement that a program can interpret, and it gives back a result that we can translate back to our informal model.
My guess is that type parameters are much better understood than type
members, but that existentials via type members are better understood
than existentials introduced by
_ or
forSome, though I’d wager
that neither form of existential is particularly well understood.
By knowing about equivalences and being able to discover more, you have a powerful tool for understanding unfamiliar aspects of Scala: just translate the problem back to what you know and think about what it means there, because the conclusion will still hold when you translate it forward. (Category theorists, eat your hearts out.)
In this vein, we will next generalize the above rule about existential methods, discovering a simple tool for determining whether two method types in general are equivalent, whereby things you know about one easily carry over to the other. We will also explore methods that cannot be written in the existential style, at least under Scala’s restrictions.
That all happens in the next part, “When are two methods alike?”.
This article was tested with Scala 2.11.7.
Unless otherwise noted, all content is licensed under a Creative Commons Attribution 3.0 Unported License.Back to blog | https://typelevel.org/blog/2015/07/13/type-members-parameters.html | CC-MAIN-2019-13 | refinedweb | 1,124 | 61.97 |
Coffeehouse Thread79 posts
David finally took down Goliath
Back to Forum: Coffeehouse
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Pagination
I'm sure all the people this month saying that IE has been decimated by Firefox/Chrome/Opera will, by next month, be saying that Microsoft's bundling of Internet Explorer makes everyone in the world too stupid to know that Firefox/Chrome/Opera exist.
HTML5 is nowhere near finalisation, you know that MS doesn't implement non-final specifications so why raise the point?
Somebody needs to relocate to Excuseville, WA.
Where is Mozilla full support for HTML5? Are they doing their usual half-assed support thinghie?
Pathetic.
What's your obession with W3bbo? He's one of the most vocal MS cynics on this board
What you are saying doesn't make any sense. Why should someone implement something that might change from one day to the other?
Internet Explorer isn't dead, not by a long shot.
The Open Web platform (HTML/CSS/JS) has to compete against Flash, not Internet Explorer or Silverlight. It's interesting that Internet Explorer's lack of adoption of HTML 5/CSS 3 strengthens Adobe's position, not Microsoft's.
and the std is not complete so they are working on it ... no one has it 100% cause it is not yet a "standard"
Won't be a standard until a couple of browsers have implemented it.. so uh- what comes first.
People may not care about or have any oppinion about the software infrastructure of a browser but what they will care about is whether their browser can run that cool page (application) that they just browsed to. - A developer feature is a user (experience) feature by proxy, whether they realize it or not.
W3C specifications only hit the final "TR" stage when there are at least two independent implementations. This does create a chicken/egg scenario for Microsoft as they won't implement specifications until they're finalised, which means it's up to the more flexible and supple development groups at Mozilla, Apple, and Opera to implement them first, which means IE will always have to play catch-up.
Microsoft needs to change their policy so they'll at least implement the major things that are unlikely to change, like rounded corners and client-side databases,
I disagree. What we're talking about here are things flash and silverlight already do and do well. People watch video through flash on YouTube and play games on PopCap with it. Cool is not a sufficent reason for non-geeks at all. Developers that implement things just to be cool will always play second fiddle to developers that actually develop for their users.
"This does create a chicken/egg scenario for Microsoft as they won't implement specifications until they're finalised,"
They won't release a version of IE which implements draft versions, that doesn't mean they don't have one or aren't working on one.
The question is whether developers will use these features and create compelling applications with them - talking about the full palette of features being implemented in browsers atm. I'm not convinced developers will not touch them because Silverlight and Flash exists.
On a personal note: HTTP and HTML are getting so overloaded with stuff... IMHO
What is HTTP getting overloaded with? The standard hasn't changed since HTTP 1.1 was finalized in 1997.
^ This, with a vengeance. I hate writing web applications. It's my job, but I hate it. I hate having to ditch smooth development of rich desktop applications in favor of having to write unreliable hacks in a language that's intended to display pages about cats rather than serve as an application framework. In order to work around the many disadvantages web applications have over rich client applications, we keep stacking more and more stuff on it, like AJAX and whatnot, and it just becomes more and more of an unworkable mess.
Whenever I'm writing a web application, the ways in which I have to stuggle and wrestle with http, HTML, Javascript and CSS to do what I want feel like I'm using a wheelbarrow to push a dead horse over a finish line.
So because we've all collectively decided that we should just keep adding to these awful outdated technologies to bring applications to the web, my job consists of pushing a dead horse over a finish line, using a wobbly wheelbarrow. Every. Single. Day.
Lately, I've opted to to try and automate our development process rather than write more web stuff. I'm actually preferring having to wrestle with the EnvDTE namespaces, rather than writing for the web. It's that bad.
doing more and more stuff ... it was designed to deliver web pages and is stateless
today we have hacked it into servering applications, having state on the server, doing web services, rss, streaming data/video/audio/other files.
sure using port 80 and http makes dealing with firewalls simple. but at some point dumping all this traffic and more on to http just gets silly. we do have other ports and we might be better served by having a few standard transports for non-html data interchnage.
not the end of the world... just seems like we have made a mess that at some point should be re-thought to make things a bit cleaner.
and possibly better with good examination of what we are doing and planning to do. | https://channel9.msdn.com/Forums/Coffeehouse/476931-David-finally-took-down-Goliath?page=2 | CC-MAIN-2017-09 | refinedweb | 952 | 61.36 |
The Assignment is:
Write a class named Car that has the following member variables:
yearModel, make, speed. In addition the class should have the following constructor and the other member functions
constructor-accept the cars year model make as arguments. an assign to the objects year, make also assign speed 0 to speed member.
Accessors to get the values stored in an object's yearModel make, speed
accelerate- should add 5 to the speed member variable each time it is called.
brake- subtract 5 from speed each time it is called.
Demonstrate the class in a program that creates a Car object and then calls the accelerate function five times. After each call to the accelerate function get the current speed of the car and display it. Then call the brake function five times after each call to the brake fuction, get the current speed. of the car and display it.
What else do i need to add to make the assignment correct, ive tried a few different things and cant get it to work.
#include <iostream> #include <cstring> #include <cctype> using namespace std; class Car { private: int YearModel; int Speed; string Make; public: Car(int, string, int); string getMake(); int getModel(); int getSpeed(); void Accelerate(); void Brake(); void displayMenu(); }; Car::Car(int YearofModel, string Makeby, int Spd) { YearModel = YearofModel; Make = Makeby; Speed = Spd; } //To get who makes the car. string Car::getMake() { return Make; } //To get the year of the car. int Car::getModel() { return YearModel; } //To holds the car actual speed. int Car::getSpeed() { return Speed; } //To increase speed by 5. void Car::Accelerate() { Speed = Speed + 5; } //To drop the speed of the car by 5. void Car::Brake() { Speed = Speed - 5; } void displayMenu() { cout <<"\n Menu\n"; cout << "----------------------------\n"; cout << "A)Accelerate the Car\n"; cout << "B)Push the Brake on the Car\n"; cout << "C)Exit the program\n\n"; cout << "Enter your choice: "; } int main() { int Speed = 0; //Start Cars speed at zero. char choice; //Menu selection cout << "The speed of the SUV is set to: " << Speed <<endl; Car first( 2007, "GMC", Speed); //Display the menu and get a valid selection do { displayMenu(); cin >> choice; while(toupper(choice) < 'A' || toupper(choice) > 'C') { cout << "Please make a choice of A or B or C:"; cin >> choice; } //Process the user's menu selection { { switch (choice) { case 'a': case 'A': cout << "You are accelerating the car. "; first.Accelerate(); break; case 'b': case 'B': cout << "You have choosen to push the brake."; first.Brake(); break; } } } }while (toupper(choice) != 'C'); return 0; } | https://www.daniweb.com/programming/software-development/threads/346139/what-do-i-need-to-do | CC-MAIN-2017-34 | refinedweb | 422 | 68.2 |
binding to local name space at startupLen Takeuchi Sep 13, 2007 5:09 PM
Hi,
I want to bind an object to local namespace at startup, similar to how datasources are bound to local namespace by specifying them in *ds.xml files. I know that it is possible to bind to the global namespace using JNDIBindingServiceMgr (in jboss-service.xml). Is it possible to bind to a local name in jboss-service.xml using some full path? For example, I want to be able to lookup java:jdbc/XXX in local namespace, is there some jndi-name I can specify in jboss-service.xml to bind to this? If not, can I achieve this through using a startup class or some other means?
Regards,
Len
1. Re: binding to local name space at startupwayne baylor Sep 14, 2007 10:09 AM (in response to Len Takeuchi)
do you want to bind to the ENC (java:comp/env/jdbc/...) or to the JVM namespace (java:/...)?
2. Re: binding to local name space at startupLen Takeuchi Sep 14, 2007 12:27 PM (in response to Len Takeuchi)
I want to bind to the ENC, i.e. the space from which EJBs typically look up datasources.
Thanks,
Len
3. Re: binding to local name space at startupwayne baylor Sep 14, 2007 1:43 PM (in response to Len Takeuchi)
you can do two things:
@Resource private DataSource ds;
or
ejb-jar.xml: <resource-ref> <description>DataSource</description> <res-ref-name>jdbc/MyDS</res-ref-name> <res-type>javax.sql.DataSource</res-type> <res-auth>Container</res-auth> </resource-ref> jboss.xml: <resource-ref> <res-ref-name>jdbc/MyDS</res-ref-name> <jndi-name>java:/MyDS</jndi-name> </resource-ref> your EJB code: Context ctx = new InitialContext(); DataSource ds = (DataSource)ctx.lookup("java:comp/env/jdbc/MyDS");
4. Re: binding to local name space at startupLen Takeuchi Sep 14, 2007 3:19 PM (in response to Len Takeuchi)
Wayne, thanks for your response. Actually, I want to bind to java:/ namespace, which is where it looks like data sources configured using *-ds.xml files wind up. I can't configure it in a ds.xml file because it is a custom data source.
Thanks,
Len
5. Re: binding to local name space at startupLen Takeuchi Sep 14, 2007 7:18 PM (in response to Len Takeuchi)
I looked at the JNDI View in jmx-console and I'm finding that I am able to bind to the java:/ namespace from the jboss-service.xml (using JNDIBindingServiceMgr mbean). But I guess I'm approaching this the wrong way since I am binding the custom data source object under the right jndi name thinking this was all that is required but in fact it also needs to be recognized as a DataSourceBinding service in order for the dependency from my EJB to the data source (in the persistence-unit definition) to be resolved.
Len | https://community.jboss.org/thread/121272?tstart=0 | CC-MAIN-2014-10 | refinedweb | 488 | 63.8 |
NAMEstrcat, strncat - concatenate two strings
SYNOPSIS
#include <string.h>
char *strcat(char *restrict dest, const char *restrict src); char *strncat(char *restrict dest, const char *restrict src, size_t n);
DESCRIPTIONThe.
As with strcat(), the resulting string in dest is always null-terminated.
If src contains n or more bytes, strncat() writes n+1 bytes.
ATTRIBUTESFor an explanation of the terms used in this section, see attributes(7).
CONFORMING TOPOSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.
NOTESSome
#include <stdint.h> #include <string.h> #include <time.h> #include <stdio.h> int main(int argc, char *argv[]) { #define LIM 4000000 char p[LIM + 1]; /* +1 for terminating null byte */ time_t base; base = time(NULL); p[0] = '\0'; for (int j = 0; j < LIM; j++) { if ((j % 10000) == 0) printf("%d %jd\n", j, (intmax_t) (time(NULL) - base)); strcat(p, "a"); } } | https://man.archlinux.org/man/strncat.3.en | CC-MAIN-2021-25 | refinedweb | 141 | 77.53 |
1.1 anton 1: /* This file defines a number of threading schemes. 2: 1.37 anton 3: Copyright (C) 1995, 1996,1997,1999,2003,2004,2005,2007 Free Software Foundation, Inc. 1.1 anton 4: 5: This file is part of Gforth. 6: 7: Gforth is free software; you can redistribute it and/or 8: modify it under the terms of the GNU General Public License 1.38.38 anton 18: along with this program; if not, see. 1.1 anton 19: 20: 21: This files defines macros for threading. Many sets of macros are 22: defined. Functionally they have only one difference: Some implement 23: direct threading, some indirect threading. The other differences are 24: just variations to help GCC generate faster code for various 25: machines. 26: 27: (Well, to tell the truth, there actually is another functional 28: difference in some pathological cases: e.g., a '!' stores into the 29: cell where the next executed word comes from; or, the next word 30: executed comes from the top-of-stack. These differences are one of 31: the reasons why GCC cannot produce the right variation by itself. We 32: chose disallowing such practices and using the added implementation 33: freedom to achieve a significant speedup, because these practices 34: are not common in Forth (I have never heard of or seen anyone using 35: them), and it is easy to circumvent problems: A control flow change 36: will flush any prefetched words; you may want to do a "0 37: drop" before that to write back the top-of-stack cache.) 38: 39: These macro sets are used in the following ways: After translation 40: to C a typical primitive looks like 41: 42: ... 43: { 44: DEF_CA 45: other declarations 46: NEXT_P0; 47: main part of the primitive 48: NEXT_P1; 49: store results to stack 50: NEXT_P2; 51: } 52: 53: DEF_CA and all the NEXT_P* together must implement NEXT; In the main 54: part the instruction pointer can be read with IP, changed with 55: INC_IP(const_inc), and the cell right behind the presently executing 56: word (i.e. the value of *IP) is accessed with NEXT_INST. 57: 58: If a primitive does not fall through the main part, it has to do the 59: rest by itself. If it changes ip, it has to redo NEXT_P0 (perhaps we 60: should define a macro SET_IP). 61: 62: Some primitives (execute, dodefer) do not end with NEXT, but with 63: EXEC(.). If NEXT_P0 has been called earlier, it has to perform 64: "ip=IP;" to ensure that ip has the right value (NEXT_P0 may change 65: it). 66: 67: Finally, there is NEXT1_P1 and NEXT1_P2, which are parts of EXEC 68: (EXEC(XT) could be defined as "cfa=XT; NEXT1_P1; NEXT1_P2;" (is this 69: true?)) and are used for making docol faster. 70: 71: We can define the ways in which these macros are used with a regular 72: expression: 73: 74: For a primitive 75: 76: DEF_CA NEXT_P0 ( IP | INC_IP | NEXT_INST | ip=...; NEXT_P0 ) * ( NEXT_P1 NEXT_P2 | EXEC(...) ) 77: 78: For a run-time routine, e.g., docol: 79: PFA1(cfa) ( NEXT_P0 NEXT | cfa=...; NEXT1_P1; NEXT1_P2 | EXEC(...) ) 80: 81: This comment does not yet describe all the dependences that the 82: macros have to satisfy. 83: 84: To organize the former ifdef chaos, each path is separated 85: This gives a quite impressive number of paths, but you clearly 86: find things that go together. 87: 88: It should be possible to organize the whole thing in a way that 89: contains less redundancy and allows a simpler description. 90: 91: */ 92: 1.36 anton 93: #if !defined(GCC_PR15242_WORKAROUND) 94: #if __GNUC__ == 3 95: /* various gcc-3.x version have problems (including PR15242) that are 96: solved with this workaround */ 97: #define GCC_PR15242_WORKAROUND 1 98: #else 99: /* other gcc versions are better off without the workaround for 100: primitives that are not relocatable */ 101: #define GCC_PR15242_WORKAROUND 0 102: #endif 103: #endif 104: 105: #if GCC_PR15242_WORKAROUND 1.29 anton 106: #define DO_GOTO goto before_goto 107: #else 108: #define DO_GOTO goto *real_ca 109: #endif 1.36 anton 110: 1.30 pazsan 111: #ifndef GOTO_ALIGN 112: #define GOTO_ALIGN 113: #endif 1.29 anton 114: 1.28 anton 115: #define GOTO(target) do {(real_ca=(target));} while(0) 116: #define NEXT_P2 do {NEXT_P1_5; DO_GOTO;} while(0) 1.32 anton 117: #define EXEC(XT) do { real_ca=EXEC1(XT); DO_GOTO;} while (0) 1.33 anton 118: #define VM_JUMP(target) do {GOTO(target);} while (0) 1.28 anton 119: #define NEXT do {DEF_CA NEXT_P1; NEXT_P2;} while(0) 1.30 pazsan 120: #define FIRST_NEXT_P2 NEXT_P1_5; GOTO_ALIGN; \ 121: before_goto: goto *real_ca; after_goto: 1.31 anton 122: #define FIRST_NEXT do {DEF_CA NEXT_P1; FIRST_NEXT_P2;} while(0) 1.28 anton 123: #define IPTOS NEXT_INST 124: 125: 1.1 anton 126: #ifdef DOUBLY_INDIRECT 1.19 pazsan 127: # ifndef DEBUG_DITC 128: # define DEBUG_DITC 0 129: # endif 130: /* define to 1 if you want to check consistency */ 1.26 pazsan 131: # define NEXT_P0 do {cfa1=cfa; cfa=*ip;} while(0) 1.23 anton 132: # define CFA cfa1 133: # define MORE_VARS Xt cfa1; 1.1 anton 134: # define IP (ip) 1.26 pazsan 135: # define SET_IP(p) do {ip=(p); cfa=*ip;} while(0) 1.1 anton 136: # define NEXT_INST (cfa) 1.26 pazsan 137: # define INC_IP(const_inc) do {cfa=IP[const_inc]; ip+=(const_inc);} while(0) 1.39 ! anton 138: # define DEF_CA Label MAYBE_UNUSED ca; 1.26 pazsan 139: # define NEXT_P1 do {\ 1.19 pazsan 140: if (DEBUG_DITC && (cfa<=vm_prims+DOESJUMP || cfa>=vm_prims+npriminfos)) \ 141: fprintf(stderr,"NEXT encountered prim %p at ip=%p\n", cfa, ip); \ 1.26 pazsan 142: ip++;} while(0) 1.28 anton 143: # define NEXT_P1_5 do {ca=**cfa; GOTO(ca);} while(0) 1.32 anton 144: # define EXEC1(XT) ({DEF_CA cfa=(XT);\ 1.19 pazsan 145: if (DEBUG_DITC && (cfa>vm_prims+DOESJUMP && cfa<vm_prims+npriminfos)) \ 1.14 anton 146: fprintf(stderr,"EXEC encountered xt %p at ip=%p, vm_prims=%p, xts=%p\n", cfa, ip, vm_prims, xts); \ 1.32 anton 147: ca=**cfa; ca;}) 1.1 anton 148: 1.16 anton 149: #elif defined(NO_IP) 150: 151: #define NEXT_P0 1.25 anton 152: # define CFA cfa 1.16 anton 153: #define SET_IP(target) assert(0) 154: #define INC_IP(n) ((void)0) 155: #define DEF_CA 156: #define NEXT_P1 1.28 anton 157: #define NEXT_P1_5 do {goto *next_code;} while(0) 1.16 anton 158: /* set next_code to the return address before performing EXEC */ 1.32 anton 159: /* original: */ 160: /* #define EXEC1(XT) do {cfa=(XT); goto **cfa;} while(0) */ 161: /* fake, to make syntax check work */ 162: #define EXEC1(XT) ({cfa=(XT); *cfa;}) 1.16 anton 163: 164: #else /* !defined(DOUBLY_INDIRECT) && !defined(NO_IP) */ 1.1 anton 165: 1.3 anton 166: #if defined(DIRECT_THREADED) 167: 1.17 anton 168: /* This lets the compiler know that cfa is dead before; we place it at 169: "goto *"s that perform direct threaded dispatch (i.e., not EXECUTE 170: etc.), and thus do not reach doers, which would use cfa; the only 171: way to a doer is through EXECUTE etc., which set the cfa 172: themselves. 173: 174: Some of these direct threaded schemes use "cfa" to hold the code 175: address in normal direct threaded code. Of course we cannot use 176: KILLS there. 177: 178: KILLS works by having an empty asm instruction, and claiming to the 179: compiler that it writes to cfa. 180: 181: KILLS is optional. You can write 182: 183: #define KILLS 184: 185: and lose just a little performance. 186: */ 187: #define KILLS asm("":"=X"(cfa)); 188: 1.39 ! anton 189: /* #warning direct threading scheme 8: cfa dead, i386 hack */ 1.1 anton 190: # define NEXT_P0 1.23 anton 191: # define CFA cfa 1.1 anton 192: # define IP (ip) 1.26 pazsan 193: # define SET_IP(p) do {ip=(p); NEXT_P0;} while(0) 1.1 anton 194: # define NEXT_INST (*IP) 1.26 pazsan 195: # define INC_IP(const_inc) do { ip+=(const_inc);} while(0) 1.1 anton 196: # define DEF_CA 197: # define NEXT_P1 (ip++) 1.28 anton 198: # define NEXT_P1_5 do {KILLS GOTO(*(ip-1));} while(0) 1.32 anton 199: # define EXEC1(XT) ({cfa=(XT); *cfa;}) 1.1 anton 200: 1.3 anton 201: /* direct threaded */ 202: #else 1.1 anton 203: /* indirect THREADED */ 1.20 anton 204: 1.39 ! anton 205: /* #warning indirect threading scheme 8: low latency,cisc */ 1.1 anton 206: # define NEXT_P0 1.23 anton 207: # define CFA cfa 1.1 anton 208: # define IP (ip) 1.26 pazsan 209: # define SET_IP(p) do {ip=(p); NEXT_P0;} while(0) 1.1 anton 210: # define NEXT_INST (*ip) 1.26 pazsan 211: # define INC_IP(const_inc) do {ip+=(const_inc);} while(0) 1.1 anton 212: # define DEF_CA 213: # define NEXT_P1 1.28 anton 214: # define NEXT_P1_5 do {cfa=*ip++; GOTO(*cfa);} while(0) 1.32 anton 215: # define EXEC1(XT) ({cfa=(XT); *cfa;}) 1.1 anton 216: 1.3 anton 217: /* indirect threaded */ 1.1 anton 218: #endif 219: 1.16 anton 220: #endif /* !defined(DOUBLY_INDIRECT) && !defined(NO_IP) */ 1.1 anton 221: | http://www.complang.tuwien.ac.at/cvsweb/cgi-bin/cvsweb/gforth/engine/threaded.h?annotate=1.39;only_with_tag=MAIN | CC-MAIN-2019-47 | refinedweb | 1,503 | 67.96 |
When I try to run the code in a scanner method, I type the number in but it doesn't show the number in words.
When I try to run the code in a scanner method, I type the number in but it doesn't show the number in words.
Hello, I am trying to create a program that will convert any number from 1 to 999 from its digit representation to its word representation. But I cannot figure out how to display it after the user...
I changed the i = 0 to i = 1, it looked like it did it. Thank you so much for your help.
it runs:
computers
omputersc
mputersco
puterscom
uterscomp
terscompu
erscomput
rscompute
Then what?
I'm not sure, I am lost at what to do next. Do you think you can fix the code?
public class WordRectangle {
/**
* @param args the command line arguments
*/
public static void main(String[] args) {
//Declare variables
int count...
All I got it to work but... how would I loop it to make that word only have to right rows and columns for the specific word. Ex computers, 9 rows, 9 columns? Here is the code so far:
package...
On what line would I do that?
How would I add it to the end?
It outputs:
computers
omputers
mputers
puters
uters
And, no that is not what I want.
Ok I'm trying to figure this out......
Here is what I have so far.... can you show me an example of what to do?
package wordrectangle;
import javax.swing.JOptionPane;
import java.lang.String;...
I just don't know where they would go in my program.
Um, I am sorry, I understand the methods, really I do, this is all I have so far, could you please show me how to do it. My teacher doesn't teach us at all how to do these things and I am so stuck...
Um, I understand those methods but I don't know where to start.
When you enter a word it will display it as a regular word then shift a letter to the right, and it will be in rows and columns for the amount of letters the word has. Example:
COMPUTERS...
Hello, I was wondering how to create the code for a word rectangle in java?
Ok, I got the loop done but.... when I hit 1 the first time, it works well but when the program runs the second, I hit 1 to the second time and it exits the program. I don't know why.
Here is the...
Thanks, but what do i state if if they hit another number?
Sorry, I mean enter another word using the number 1.
Hello, I made a program called count vowels and I finished it but I want to ask the user to enter another number by pressing the number 1 and any other number entered would be invalid. I use...
All right, thank you for your help.
Well, I tried it again but I am outputting: "Therefore, x equals: 4992.333333333333." so I am close.
Here is the problem.
Two girls agree to go on a road trip together. They travel (x + 5)km on...
I tried to do it but it wouldn't print it out. Um, can you think of code that might work? Please?
All right I included it in x. Now where do i go from this code???
package fridaybonusquestion;
public class FridayBonusQuestion {
/**
* @param args the command line arguments
... | http://www.javaprogrammingforums.com/search.php?s=4b4024b9dc0532ee6831093890d22122&searchid=477468 | CC-MAIN-2013-20 | refinedweb | 584 | 84.37 |
Programming Reference/Librarys
Question & Answer
Q&A is closed
Variables
Variables are the means of storing data in a program. Say you want to make a calculator, you need to use variables. Say you want to make a program that takes in a word and then modifies it, you need to use variables. Variables can be created and “destroyed”(deconstructing comes later on so don't get your hopes up). The value or information that they store can be changed and in some cases, that you make it so, cannot be. Except for the syntax of the language, you are in control!
To create a variable:
//don't worry about things that have a " * " in the comment, we'll get to those #include iostream //a pre-processor command * using namespace std ; //a declaration of the namespace used * int main() //the main function * { int var1 ; //the declaration and naming of a variable return 0 ; //value return statement * system ("pause") ; //a system command telling the screen to pause (freeze whatever is on the screen, don't worry not your computer) *
That is your first program! It doesn't do much though.
Let's analyse the declaration and naming of the variable:
int var1 ;
The syntax of naming a variable is the following [varaible type] [varaible name]
The name of the variable can be whatever you want, except a number, but it is good programming practice to make it a descriptive title corresponding to what the variable stores.
This is a list of the most common types of variables:
bool Stores either value true or false. char Typically a single octet(one byte). This is an integer type. (one character) int The most natural size of integer for the machine. (a whole number) float A single-precision floating point value. (stores a decimal number) double A double-precision floating point value. (stores a decimal number) void Represents the absence of type. wchar_t A wide character type.
Now you have allocated memory for the varaible. That is just reserving space for it. You haven't set the value of it yet. When you do, then the space is filled.
Our variable was an “int” or, in Enlish, an integer. Let's make the variable equal to a number.
int var1 ; var1 = 5 ;
The variable var1 now equals 5. You could also set the value when you declare it like such:
int var1 = 5 ;
Variables can even be equal to each other!
int var1 = 6 ; int var2 ; //another integer variable named "var2" var2 = var1 ; //the value of var2 is now the same as the value of var1
Useful Tip When making a variable equal to something, you must use this syntax: [the varaible that you want to change] = [the number or existing varaible] ; | https://code-reference.com/cpp/variables | CC-MAIN-2020-34 | refinedweb | 458 | 71.14 |
I’m trying to write a few unit tests for Vue and instead of setting up a new wrapper each time, I’d like to use beforeEach() to take care of it automatically. When I run the debugger, it fails all of the tests, then runs the beforeEach() function for each of the tests.
This is my .spec.js file.
import { mount, } from '@vue/test-utils'; import QcAddressView from './address-view.vue'; const id = 'test_address-view'; describe('qc-address-view', () => { let wrapper = null beforeEach(() => { console.log("beforeEach executed!"); wrapper = mount(QcAddressView, { id, address: { addrLine1: '111 Testerson Way', addrLine2: '', cityName: 'Olympia', stateCode: 'WA', zipCode: '98512', countyName: 'Thurston', countryName: 'United States of America', }, }) }) test('sets up a valid address', () => { console.log('sets up a valid address'); expect(wrapper.attributes('id')).toBe(id); }) });
The console shows me the test fails:
FAIL: qc-address-view × sets up a valid address (72ms) TypeError: Cannot read property 'addrLine1' of undefined TypeError: Cannot read property 'attributes' of null
It can’t read the properties because beforeEach() hasn’t set up the object yet.
Then it runs beforeEach() after the test instead of before it:
console.log: beforeEach executed!
When I tried it with three tests, it would fail each test, then console.log would print "beforeEach executed!" three times.
How do I get beforeEach() to run before each test, instead of each one after all?
beforeEach is actually running before your tests. Otherwise,
wrapper would be
null in your test, and you’d get a different error.
You’re seeing the console logs after the test because Jest buffers the log output, and dumps it at the end of the tests. You can avoid the bufferring by setting
useStderr. You can do this from
jest.config.js:
module.exports = { useStderr: true, }
###
The answer was to put the
id and
address into an
attrs object, thus:
wrapper = mount(QcAddressView, { attrs: { id, address: { addrLine1: '111 Testerson Way', addrLine2: '', cityName: 'Olympia', stateCode: 'WA', zipCode: '98512', countyName: 'Thurston', countryName: 'United States of America', }, } }) | https://exceptionshub.com/vue-unit-test-beforeeach-executing-after-all-tests-not-before-each-test.html | CC-MAIN-2021-49 | refinedweb | 332 | 55.54 |
1200 QThreads need create
this code doesn't work on linux.
it makes
QThread::start: Thread creation error: resource temporarily unavailable
after ulimit -s 1024
GLib-ERROR **: Cannot create pipe main loop wake-up: too many files open
@#include <QtGui>
class MyThread : public QThread {
Q_OBJECT
private:
int m_nValue;
public:
MyThread() : m_nValue(1000)
{
}
void run() {
while (true) {
msleep(m_nValue);
//qDebug() << QThread::currentThreadId();
}
}
};
int main(int argc, char** argv)
{
QApplication app(argc, argv);
MyThread *thread; for (int i=0;i<1201;++i){
thread=new MyThread();
thread->start();
qDebug() << i;
}
return app.exec();
}
#include "main.moc"
@
Well, 1200 threads is overkill of course and it certainly won't do much for your application. It's better to use a thread pool (usually processor count or processor count + 1 threads) and handle the tasks there. Look into QtConcurrent if you just want a lot of tasks done.
in Windows that code is run good.
my app needs more than 1200 threads, 1200 just for test.
and.. above code runs on linux very well, and build 5000 threads!
@#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <signal.h>
#define NUM_THREADS 5000
volatile int while_condition = 1;
void sig_handler(int signal)
{
while_condition = 0;
}
void *do_work(void *ptr) {
size_t i = (size_t)ptr;
while (while_condition) {
sleep(1);
}
pthread_exit(NULL);
}
int main(int argc, char** argv) {
pthread_t threads[NUM_THREADS];
pthread_attr_t attr;
void *ptr;
size_t i;
signal(SIGINT, sig_handler); /* Initialize and set thread detached attribute */ pthread_attr_init(&attr); pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE); for (i = 0; i < NUM_THREADS; ++i) { printf("In main: creating thread %ld\n", i); int rc = pthread_create(&threads[i], &attr, do_work, (void *)i); if (rc) { printf("ERROR; return code from pthread_create() is %d\n", rc); exit(-1); } } /* Free attribute and wait for the other threads */ pthread_attr_destroy(&attr); for (i = 0; i < NUM_THREADS; ++i) { int rc = pthread_join(threads[i], &ptr); if (rc) { printf("ERROR; return code from pthread_join() is %d\n", rc); exit(-1); } printf("In main: stopped thread %ld\n", i); } return (EXIT_SUCCESS);
}@
- tobias.hunger Moderators
Of course you should be able to run an arbitrary number of threads at the same time. But you can never ever run more than threads at the same time than you have processing units. It does sometimes make sense to run more than that number of threads, but only if the threads are not CPU bound (e.g. have to wait for data from the HDD).
You further need to be aware that creating and destructing threads is a somewhat expensive operation. That is the reason for systems using thread pools consisting of a fixed number of threads. These threads are then used to process jobs that get queued with the system. This allows to queue lots of jobs while keeping the thread management overhead low.
QtConcurrent is such a thread pool concept.
See the forum thread "Help With this ERROR:QThread::start: Thread creation error: Resource temporarily unavailable": for a discussion of the same problem.
There is a limit on the maximum number of threads a single application and/or a user can start.
As Tobias already mentioned, there it almost always does not make sense to start significantly more threads than you have CPU cores. In the worst case, the overhead of managing that much threads (by your app, by the OS) might be contra productive.
Linux has a default limit to 1024 max opened files...if you want to change it, just see /etc/security/limits.conf to change per user max files, or if you want a whole max files setting, take a look at
/proc/sys/fs/file-max and persists that in /etc/sysctl.conf
Bye
Are you sure you need exactly "threads"? Because it is stressful for OS and your application. Maybe you need something like "stackless" approach? Or on other side you may try CSP approach (lib for example:) - that is extremely effective to bypass threads limitations.
Guys... this question is almost 3 years old now... Why pull it from the grave again?
You're right, but I didn't see a valid response to resolve that problem...so in the future my response can help someone else. | https://forum.qt.io/topic/1795/1200-qthreads-need-create | CC-MAIN-2017-47 | refinedweb | 684 | 62.98 |
Join devRant
Search - "pass"
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- Wrote some codes that uses your photos to compose an input image. Will post code later. Written in Python though. Also this is my dad. Also I wrote this in Yellowstone cuz I didn't like the view lol
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- Wrote some code during the break that transform an image to the following styles, is it good enough to post on github?27
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- Zero bottles of beer on the wall, zero bottles of beer; take one down, pass it around, 65535 bottles of beer on the wall.5
- Now I lay me down to rest,
I pray I pass tomorrow's test.
If I should die before I wake,
That's one less test I'll have to take.6
- WTF your function takes in 12 parameters!!! Then it checks one and pass the rest to another function!!12
- When you are doing dijkstra every 5 fucking second trying to pass the guy in front of you while walking.4
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- I told my colleague today that he didn't pass the Turing Test.
He did not understand.
Which proves my point.
- Rewriting my resume to pass the algorithm for a job IDENTICAL to mine in responsibilty, but with fewer hours and more pay...
Due by Thursday. Wish me luck8
-
- Since git, sometimes I drink and code until I pass out
Today I woke up with good working code that I don’t even remember writing5
-
- My dad said if I fix his old car then I can have it once I pass my driving test. I can't seem to find the source code...18
-
-
- *
- Flyer: "Looking for someone to code for coffee factory-thingy, we will not pay you in cash."
Me: "Fucking Pass!"
Flyer: "-We will pay you in bags of coffee instead, from itally"
Me: "-me that pen and sign me up!"1
- Yea so I was creating registration form and I did this:
...
if ($pass != $passrepeat or
$passrepeat != $pass) {
# MAGIC
}
...
I think I should quit being a programmer..14
- Hey man can you fix my tv, computer, toaster, phone, or hack this phone i found, can you hack me a wifi, can you make me a website/app i have a really good idea. (For free of course)
Hey man you only need a good idea for an app then become rich.
(Insert countless of other retarded requests here)
Someone kill me6
-
- Making a meme to pass the time...
All this waiting, only because I wanted to try one small thing -.-
Oh boy, JPEG compression strikes again...
Wish I could upload pngs. Then I could use alpha channel too.4
- Me: i have to pass this test tomorrow so I better study
Me to me: start an overambitious project that will take years to complete3
- Me: I should try out Figma's vector tool
[30 minutes pass, this happened]
Pros: its nice
Cons: not as intuitive as Illustrator's or Inkscape's....
AND MUH GRIDS17
- Yet another nice (bad) tool with a funny name: volkswagen
> Volkswagen detects when your tests are being run in a CI server, and makes them pass.
LOO
- I wish there is such thing as branch in a relationship. So that whenever a couple are having a fight, they can create a branch and work their shit out in that branch and eventually merge to the master branch.
Wait
Merge....
That just costs.... more conflicts3
-
-
- Me: Wish I got one guilty free murder pass..
God: GRANTED! Which software tester would you like to kill?4
- Some former colleague just blatantly commented out units tests I wrote for his build to pass. What the...7
- I should find me a girl that loves to code. Those would be some arguments I would like to pass through4
- So I finished my personal website. It works fine on every browser... Except IE. All JS functions pass the compatibility check and I don't get any errors. Great.6
- Finally installed Ubuntu and successfully configured the wifi setting, any package I should install?34
- Just finished swapping soft tubes for rigid ones.
Bending was a lot of fun :)
It's 4am, but I don't think I'll be able to sleep waiting for the leak test to pass13
-
- Well, after two hours of scratching my head, I found that angular.isNumber () returns true when you pass in a NaN. Brilliant.2
-
-
-
-
- Even during games, I find bugs in it...
Just found NULL in FIFA GAME.
Wonder which object failed to pass it's value2
- Went to a hackathon yesterday... WITHOUT HAVING AN ENTRY PASS 😛😛 made a hot product.. Pitched it.. Got disqualified when pitching(they found it halfway during the pitch... took them 2 days to figure our play there)😎😎3
- So... We lost power here.
Why now?? I have work to do!!
I guess I get a free pass to scroll through Devrant for the next few hours.4
-
- Continuation of rant...
I PASSED THE TEST!!!!! YEAHHHHH
Now only an interview left. Please....
If i fail this interview, no more tries.
Wish me luck.
From this point, all personal projects and requests will stop
-
-
-
- 2 situations when you are equally fucked :
1. It should have failed here, why is it passing?! 😯
2. It should have passed here, why is it failing?! 😯
- Doing Google foobar level 2 i LOVE IT its harder then normal tests and even you get a interview with google when you pass level 5 wohooooooo.11
-
- I was looking through some old robotics code from the team I am on and I found this:
Void ArcadeDrive(xspeed, zrotation){
Drive::ArcadeDrive(zrotation, xspeed);
}
Why?
Why not just pass in variables in the opposite order?3
- I love TDD.
It's so relaxing to know that your fix didn't fuck up anything else when the tests pass.1
- Had a job interview for a front end dev (Involving a technical test). After couple of days, recruiter says - Unfortunately they say that you are too focused on best practices so they want to pass.4
- In the uni at an exam:
Professor: I can't let you pass.
Student: Can't you ask me something?
P: I can lose my job if I let you pass5
-
- I fucking hate the fact that every tech company now needs for devs to be up-to-date with geeksforgeeks or leetcode to pass their interview.
Is there no other way to confirm that a Dev is legit?8
- OS : Tail OS ✓
pass : 16+ ✓
Update password : every 15 days ✓
Mac address : spoofing ✓
Then you realise
Your Aadhar information is in gov DB.14
- Pass by reference, do not wrap needlessly
// Bad
takesCallback(function (data) {
// Literally all this function does
processData(data)
}
// Good
takesCallback(processData)
I see this all the time, especially with jr devs.8
-
- Python tip: some python functions have **kwarts (key-word) arguments, that means you can construct your parameter dictionary like so:
kwargs = { 'a':1, 'b':2}
And pass those arguments like so:
function(**kwargs)9
- Client send email ... (15 seconds pass) ... client sends IM/Slack ... (15 seconds pass) ... client calls.
Me: Yes?
Client: Did you get my email asking how the project is coming along? Also, can you do this <totally unrelated> thing that will sidetrack you for 2 hours?3
- bladder: I got to pee.
me: NO! To deep in code zone.
[20 mins pass]
bladder: I got to pee.
me: NO! Let me finish this.
[30 mins pass]
bladder: I'VE GOT TO PEE
me: NO! In a zone.
[5 mins pass]
bladder: GO! GO! GO!
me: D**n you bladder.
I hate this game. I lose every time.7
- Unit tests fail.
Re-ran it again without looking at details.
Unit tests pass now.
What. Why?!
Now I can't sleep at night.6
- !student
Principles of Programming Languages teacher:
No one in industry uses git.
The same guy who refused to take semester project submissions as github links.
Also "Python is never pass by reference/id()"5
- my dad just told me to open the ports of a NAS that has admin:admin123 login. that NAS contains all of our backups and more.... YEAH NO9
- Was fired after 3 months. My boss said "how did you even pass engineering school?!"
I'm not a skilled programmer... and never will be!6
- Idk if anyone here noticed.... sudo sounds like 速度 in Chinese, which means quickly. So the every time I use this command I just feel like I'm rushing computer to do something for me5
- Our team is developing a online e-commerce application. Since the owner uses Last Pass and doesn't like the extension icon in input fields, he asks the developer team to install the extension and ensure Last Pass was disabled for all input fields, password and usernames included, across the site. It was unacceptable to ask him to disable it though the extension menu.6
- Articles 13 and 11 pass exactly during the world cup, so news channels won't report on it coz they're too busy showing Ronaldo's goal for the 376th time10
-
-
- -"Need to install a program, but dont have a browser!"
-"Use other computer and USB stick"
-"Do i pass the icon?"2
- So, what are you all working on right now? Let's get some screen-shots in here!
I'm working on my "BrowserBandit" software - it reads a firefox or chrome profile and extracts saved user/pass combos, history, and autocomplete entries.19
- Just failed at 4/6 subjects at my uni. And now I have to study subjects I have completely no interest in just to pass. I feel depressed2
- - Why isn't this script working
- Review Error Log
"Incorrect Syntax: line 122"
- There is no line 122
**3 Hours Pass
- Damn had an old broken version of the script still running in the background 😐🔫
- While Google is developing breakthrough AI systems that might quite possibly pass the Turing tests in the near future, my university suggests I learn JQUERY and calls the course Advanced Web Programming
- New Year resolution 2018:
Actually read / pass at least 2-3 of the 100+ books/courses on professional topics that I bought in 2017.
And stop buying stuff I don't use.3
- When one of CS teachers went to jail for asking money to pass exams.
Defiently an experience for both him and students.2
- Fuck you for imposing the upper limit on password length for my online banking! Why do you even care about my pass - don't you fucking hash it beforehand?!3
-
-
- Function bool NewSpeedTestingStandard()
{
AskUserToLoadAPage();
return UserUsesPhoneWhileLoad()
? "Fail" : "Pass";
}8
- Back with more features now!
Cuz I don't have anything to do at work
This image is composed of screenshots from season three4
- Seriously. FUCK MATH. I've been coding for more than 4 years. Never did I use complex mathematics.
And now I'm supposed to pass math exams. Haven't used that shit since high school. Fucking fuck3
-
- When the devs "fix" the unit tests by modifying the test cases so they pass.... Bugs are still there, but our deployment succeeds now. Oh federation....2
- Moving to a new job 5 months after starting the previous one. The company did not manage to pass my probation period.5
-
- 99 little bugs in the code
99 little bugs
Take one down and pass it around
127 little bugs in the code2
- WARNING: No coding was used here
Once I was 10 (6 years ago) in primary school we had library databasesystem on a computer and I was in charge on maintaining the library on a normal account. But I found that I could login as Administrator using password “password”. I told friends about it and it somehow got to the teacher. After that I was in the headmasters room. Wasn’t expelled though 😉😃. It was one of the coolest stuff and funniest discovering the pass.
- In a programming exam, we had to write a program in 60 minutes, part of which was sorting some strings by length (strings the same length had to be in the same line)... I had like 3 minutes left, so i wrote this beauty:
boolean b = false;
for(int i = 0; i <= 999999; i++){
for(int j = 0; j <= strings.length; j++){
if(i == strings[j].length()){
System.out.print(s + " ");
b = true;
}
}
if(b){
System.out.println();
b = false;
}
}6
-
-
- Submiting a form with Ajax without e.preventDefault()
Chrome : Yeah it's all good
Firefox : No. Eat shit. Display a length error in console...
IE : I'll let you pass but I'll crash right after...
I'll never forget again
-
- 99 IT recruiters on the phone, 99 IT recruiters.
Take one down and pass it around, 99 IT recruiters on the phone.3
-
-
- Ugh all but one unit test is passing :-(. I know the code is working- so the problem must be in the test... [add @ignore to test]. Yay they all pass now!1
- Who are you, developers who send out their cv in a word document and in a language that is not English???🤯 May I tell the HR to not pass any of those CVs to me?6
- my worst dev sin:
Commit and go home on a friday not waiting for the build to pass.
Tons of notification from counterparts the following monday1
-
- An update on my rant about that interview I had.
They emailed saying they're sorry I didn't pass etc.
My literal response was: wow. Shocker. No shit I didn't pass 😂
- I dont really have a story here, i just want to thank every college teacher/assistant teacher who has real world experience and decides to pass it on to students instead of picking from the billions of job offerings.3
- My mother is watching some turkish romantic bullshit and there are "hackers" who chat in "" i cringed while going pass the TV.
-
- I'm mainly a Java guy but JS ability to pass a function has a parameter to another function makes me feel like god.5
-4
- No man's sky: I can imagine the devs fighting management and marketing letting them know that what they were selling was bullshit and they be like 0 fucks given.2
-
-
-
-
-
-
-
- 1.Pass my final tests (A levels -> i think thats the name of them in usa)
2.Get to university
3.Finish my private projects (at least few of them)
4.Learn more programming, electronics, ect.
-
- We all know that scumbag test that sporadically decides to fail. Simply running it again makes it pass.1
-
- I got a few resolution for this year.
-Releasing the app I am developing
-Learn more about devOps
-Learn machine learning
-primarily, pass out from this college without hurdle
-
-
- "In this API you need to pass the epoch in user's timezone."
WTF!! can this world be any worse...... how many epochs are there in this world?4
- Having an app doesn't give you a free pass to have a website that works horribly on mobile.
I'm looking at you, Mint.2
-
-
-
- !!rant
I just hate job ads which have a pseudo-language (Java or C for ex) code snippet inviting you for an interview.
Oh my God they are so fucking LAME. I actually pass on these job offers.1
- That moment when you are about to pass out because you are so hungry, but you want to finish this module before you leave your PC.1
- I've been meaning to mention for the pass three months that my Java Programming class has "Leet" in it's course number.
-
-
- I think YouTube is trying to tell me something. I think I'll pass though, I don't really fancy working at such a massive company.1
- Anyone ever had exams, where teacher tell you that if you study on said part of the course and you'll pass, then got completely blindsided on the actual exam... Oh the horror 😂6
-
- I want to buy a beer for everyone who developed the mobile pass app. Just breezed through immigration and customs without waiting in the 1 hour+ line. Technology wins. Cheers
-
- Thursday: Made an appointment with doctor for (painful because no anesthesia) outpatient procedure. Sent message to team slack saying appointment would interrupt part of my day.
Friday: Boss decides to launch website. Launched.
Saturday: Fixed many broken things.
Sunday: Fixed more broken things.
Monday morning: Texted team about fixing more broken things WHILE BEING OPERATED ON!!!!!!!!!
Monday afternoon and evening: STILL WORKING ON MORE BUG FIXES!!!!!!!7
-
-
-
- Having to explain to asp classic developers why you shouldn't try to pass a DataRow to an MVC view
😭6
- 88 hours on the clock
Take one more, pass it around
89 hours on the clock
Maybe my goal next week should be to clear 100 😂5
-
-
- Is it worth taking the insanely expensive Oracle Java certification test as a self taught high school student? I know I can pass if I study more, but will it make me look better?2
-
- This book I'm reading on SEO is like drinking nightquil.
The more I read the harder it gets to not pass out.6
-
- How do clients not remember crucial things like admin user+pass because we get hired to fix your shit not your damn admin cradentials1
- Youtube with its annoying ads that pass my dns server. Well, no longer! Just add /api/stats/ads to the universal routing. Poof ads gone ^^,2
- Want to get last value of a list?
value = 0
for value in list:
pass
working with 10 year old code :/3
- #include<semester.h>
#include<tension.h>
void pain()
{
mind=confused;
while(study!=done)
{
paper = back;
parents=scold;
}
if(i==pass)
{
tension free;
}
else
{
go to hell;
}9
- trying to login fb
username : ...........
pass : ...................
without thinking just type that pass
error changed pass 2 year back
again try to remember same password
:(
unable to remember1
- Python abstract classes... Looks like a pain in the ass...
I'm just gonna create a class filled with methods that just pass or throws NotImplementedException
Good enough?2
- Hey guys, for those who still use facebook.
I've created a web extension which removes "popular across Facebook" and sponsored posts from facebook feed. Check it
- $ python
>>> class Object:
>>> pass
>>> self = Object()
>>> self.attr = val...
>>> * copy paste code from some class
<Ctrl>+d
Testing ☑️
- One project deadline coming up, one presentation to be given next week, and 3 exams on consecutive days.
Scared as fuck. 😭
I hope I pass.
Wish me luck!2
- Job requirement for mee position opening in 11 days: CISSP...
I want this job. Anyone have tips on how to pass this exam in a week?4
-
- If you bought a new phone in 2018, why?
And why did you get that *model/brand*?
If company phone, then why not just pass?14
- I just went to pee and I spent like 10 minutes reading devrant and I got paid for it.
Yes I pee sitting
-
-
- Was supposed to take my midterms today, while my mates were supposed to pass their assignments.....few minutes before the class we saw the dean running telling the students to go home/leave. Turns out there was a “bomb threat”....4
- Had to play with old code of mine today. I wrote when I just started working a few years ago. Had a bit of shame be mostly a good laugh at pass me. Dam I used to be bad1
- ~learn react enough to make a full-stack web app
~learn Flutter
~get good enough at data structures and algorithms to pass a fucking coding skills test
- I finish my internship in dev the next week and my supervisor wants to hire me as a Business Analyst, for that I have to pass some tests in an assessment center.. I hope I will success it ! 👊1
-
-
- This guys in my college talk so much about hacking and make it look like its so cool and all they tell is how to trick your neighbours to make them 'give away' their pass.2
- Hang the fuck on Microsoft... Isn't the whole point of a season pass to get DLC...
I smell a money grub!
- How to pass yourself off as a Web Developer.
Download Wordpress.
Install theme.
Install plugins.
Activate plugins.
Customize theme.
Receive sum of $10,000.6
- Right...
So some asshole just tried to charge me 200 euro paid to Plugin Media Group A.G.
Couldn't get pass 3ds but still...
If you have made an order with OnePlus cancel your card. Today2
- Anyone here here has used pluralsight? Really powerful platform for learning IT stuff, I have learned tons with it4
-
-.
-
- !rant
Paradoxon: if an AI gets good enough to pass the touring test, it would also be good enough to _not_ pass it 🤔7
- started with
printf("Hello World... It's 2010")
Journey to
cout
println
Document.write
echo
Stayed at
try:
print('hey there...')
except:
print('got issue.... Fu#k this bug')
pass
-
-
- Listening to Kavinsky and having the urge to do some coding in 80's atmosphere , then remembering semester starts in two days and I really gotta pass those courses. *sigh*
- Pluralsight said I'm in the 85th percentile of people who know JavaScript and therefore I'm an ”Expert"
So now I walk around like, "bro do you even know how to pass a callback?" 😏
- I didn't clear my exam. Now it's my last chance have to pass at least in 4 subjects from 8 boring subjects otherwise I will be detained 😥 I hate fucking theory and fucking maths 😭
-
- "Coding and testing of the iOS app will be done tomorrow. Then we need to sign and publish it + pass review so it might be live this time next year"1
- 23 machines down, 50 days lab access left. Hope I'll pass the exam on November and become an OSCP.2
- Perfect use of DI in .NET Core project.
> Passed logger object in UI project's controller class constructor.
> Then pass it to internal class.
> Then pass it to business project.
> Then pass it to another class and finally used logger in a method to log exceptions in try-catch1
-
- So this "senior" programmer tells me that redux should only connect to the upmost react component and then IT should pass props down..... Like why even use redux then? WTF1
-
- Just need to pass this json object to the controller as a string. Cool just a quick two minute job.
Three hours later and it's still passing null, what the apple fuckery is your problem?!
- mysqldump db > db.sql
yum install mariadb
*config*
mysql -u username --password pass db < db.sql
Why do I control mariadb with the mysql word? I installed it, I want to use it....2
- Stumbled across a gist showing how to pass cli arguments to gulp tasks, suddenly found myself resisting the urge to cover every single line of the gulpfile in switches and arguments
- A team blacklisted a series of words in order to prevent XSS. Obviously they failed terribly. Like they filtered 'alert(' and crap like that. Like a hacker is going to alert stuff using xss. I opened a bug to their team.1
- I fucking hate the Nginx Ingress Controller for Kubernetes. Fucking piece of shit. You fucking can't do a fucking simple rewrite and proxy pass???? Fucccck!1
- It's 2016 and I have to learn SQLJ to pass a subject.
Yes, I'm unfortunately a part of the "great" Indian education system.6
- - read motivational quotes
- noticing that it’s not applicable or having any motivational effect whatsoever
- listening to music while pondering what is my purpose of living (aside from passing butter)
- try to think positive (imagining my next grand vacation which I don’t have the money for, yet)
- sudden realization that I have no actual plans for the future (though it may not be bleak, it doesn’t seem to be bright either)
- try to think of all my little accomplishments so far
- ends up with me being complacent and slightly determined to survive the office for another day
...
...
...
Nvm the above, usually it’s either playing some games or enjoying a nice food, whichever is more convenient at the time,3
-
- When I study just to pass tests, I'm a bad student. When I write software to pass tests, I'm a good developer. 🤔
-
-
- #include <midsemester.h>
#include<tension.h>
Void pain()
{
Mind=confused;
While(study!=done)
}
Paper=blank;
Parents=scold++;
{
if(i==pass)
tension free;
else
Dad's belt;
}
.
.
OUTPUT:
compilation error....Engineering detected.
- Hail Mary pass: writing your web app in one single streak, refresh the index, and get http 500 OK 🙏🙌3
-
- New project, make a simple change, a load of tests fail, stash changes to see if they ever passed, rerun tests: they pass ... rubbish must have been something i did. unstash changes, rerun tests to check the details: they pass ... walk away slowly
-
-
- What. Setproctitle actually changes /proc/PID/cmdline? Who thought that was a good idea? Now a bunch of people at my "security" company think that makes the command line a safe way to pass secrets.1
- When you’re too lazy to figure out callbacks so you just pass a function as an argument to a function as an argument to a function 😂😂😂7
-
-!
- One QA guy ... I solved one ticket out of two. He doesn't want to pass it because the other one is still unfixed.
- Is there a way to dynamically change your IP address while scraping website so that you don't get blocked cojstantly
- Just spent an hour trying to work out why changes to the database weren't saving. Forgot to pass the context from the unit of work to the repository.
Sometimes I hate myself.
-
- Job hunting again is so fucking hard, they should tell you right away if you did not pass , instead of keep your hopes up. I can take the rejection but the anticipation for nothing really hurts.2
- Well, the new audit tool in the chrome dev tools seems to be nice and shiny, but even google does not pass its tests completly...3
- I have this specific friend who says he doesn't have time to learn C++ to pass project labs in uni.. but 2 days later messages me drunk from a bar saying he have been drinking for past 9 hours.3
- When your redirect url passed as get parameter to 'secure' the login you pass bade64 envoded string with path, length and (salted) md5 hash ....
why God why you secure a redirect you do 302 to on success1
- Security issues I encountered:
- Passwords stored as plain text until last year.
- Sensitive data over http until last year.
- Webservice without user/pass authentication.
-
- Instead of segfaulting xmllib2 just completely destroys your XML file if you pass a null to the writer.
Debugging that was lovely :[
- Some day I'll replace all my function return values of type int and string with either 42 or "foobar" just to see how many of my unit tests still pass.
-
- When the team you inherit the project off of can't even be bothered to add a parameter to their constructor. Instead they expect you to pass it in as part of a title string :')2
- Informal python poll:
Do you put your __init__ functions at the top or bottom of your classes?
AKA:
class myClass:
def mymethod(self, arg):
pass
def __init__(self):
pass
or...
class myClass:
def __init__(self):
pass
def mymethod(self, arg):
pass5
- Finish the story and all tests pass
*notification another merge request been approved
Pull changes build, all tests faill
- I really can't understand NodeJS. Why sometimes I require the same module in several files and sometimes I've to pass it as a parameter in the module.exports function of the other file? Where the hell I learn all this shit?5
-
-
-
- I got one problem I have some data in local storage. Now i have set iframe with another website. I need to pass local data into form inside iframe. but it gives me Cross Site permission issue. Any suggestions.
-
- Does anybody know if there's a tool for parsing protobuf using live Network capture? I basically want to be able to pass profiles into something like Wireshark and get a live request response cycle1
-
- Feeling stupid as fuck in a group programming with our lead engineer (and Im the one driving). Tell me Im not useless :(1
-
-
- Today I pass an assessment test to be hire as Business Analyst / Business Intelligence, I'm stressed about it because I'm just finishing the school, I got this possibility because I made a really good internship1
-
-
-
- "This is an easy task, call me when it's done"
5 months later
"well the test of senduser didn't pass"
Me: "this wasn't on the docu"
"oh, let me rewrite it"
- Convert any SlideShare slide into PDF format in one click. Time pass project...
- Dat $15 dollar game maker humble bundle, I dont know if I will ever need it but damn it feels gud.1
- Just applied for my next school, I'm going to study application development. Lets hope for the best and hope that I pass my exams and get accepted.1
- How do you guys calculate complementary color?
I feel like I have a good algorithm but I also feel like I've been posting too much recently so I just want to know what you guys do to calculate complementary color.3
- I used original calls to rest services in order to pass my junits and increase code coverage.... :-P
- def examMonth():
for exam in exams:
while days:
if time ≥ week:
pass
elif time == days_3 or time == days_2:
book = open_book()
study(book)
else:
panic_and_devRant()
days = days - 1
def study(book):
see_open_book()
delay(minutes_10)
devRant()
-
- am trying to pass an array of php to js for use with beforeshowday function in datepicker. any suggestions?4
- Just wondering any of you has seen automated tests in a CI machine? Theyre not reliable enough to be running all the time because many times its just an empty error amd its tedious to investigate and wastes lots of time2
-
- Single Sign on Authentication for a growing product suite? Sure, just validate the user's credentials in the dashboard and then pass their role to the product's web app via query parameter. No need for tokens or an auth server!
-
-
-
- I fucking hate Ops!!!
I spent the fucking day trying to understand why the fuck the AZURE the firewall blocks me on port 8000 while i let me pass on port 8001.... men i hate "not" having an ops....
- Learned just enough Groovy to call a Python script and pass args to it. I have no problem with that.
Top Tags | https://devrant.com/search?term=pass | CC-MAIN-2019-09 | refinedweb | 5,172 | 73.58 |
53666/how-to-create-singleton-classes-in-scala
Hey,
Scala introduces a new object keyword, which is used to represent Singleton classes. These are the class with just one instance and their method can be thought of as similar to Java's static methods.
Here is a Singleton class in Scala:
package test
object Singleton{
def sum(l: List[Int]): Int = l.sum
}
This sum method is available globally, and can be referred to, or imported, as the test.Singleton.sum. A singleton object in Scala can also extend classes and traits.
scala> val rdd1 = sc.parallelize(List(1,2,3,4,5)) - Creating ...READ MORE
You have to install Intellij with scala plugin. ...READ MORE
val coder: (Int => String) = v ...READ MORE
Function Definition :
def test():Unit{
var a=10
var b=20
var c=a+b
}
calling ..,
You can check this example in your ...READ MORE
Hi,
To create an RDD from external file ...READ MORE
OR
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Hi there, if I call a double function like
double MyPrice( ) { return cost; }
(value "cost" assumed to be set to 7.00 why this function returns 7 and not 7.00?
thank you
How do you know if it returns 7 or 7.00?
Do you print a double or an int?
When you convert the MyPrice return to an int, it'll become 7.
Post some more code?
It is as Hiddepolen is saying, right now you have the function:
double MyPrice(){
return cost;
}
so it returns a double value.
If it is however that the variable that it's being returned to is an int,
when you print that variable you will only print the 7;
eg. int x = MyPrice ();
printf ("%d", x);
that will only print the 7, whereas if you had:
eg. double x = MyPrice ();
printf ("%f", x); // OR printf ("%lf", x);
that would print: 7.000000
NOTE: to reduce the zeros ( printf ("%.2f", x); )
Hi ya, no I don't convert it into an int. If I replace that 7.00 with say 7.01 then when the function returns it will return 7.01. So for some reasons when it is 7.00 it chops off the .00.
The variable cost has been declared as double. I have another function that sets the cost, say something like
void setCost( double Cost ) { cost = Cost; //cost is a double here }
I pass a value of 7.00 to this function and then somewhere else in main I call the double MyPrice function so it should return 7.00 and not 7. As I said above if I change that 7.00 to 7.01 or any other value as long as the last digit is not 0 will return fine. So say 7.02 etc.
Strange. Could you post your entire code? Or at least all the relevant parts, everything to do with those two functions and the printing of the double.
Cheers
hi there, sure here is an example:
#include<iostream> using namespace std; double cost; double getCost( ) { return cost ; } void setCost( double Cost ) { cost = Cost ; } int main() { double myCost = 0.0 ; cout << "What's the cost? "; cin >> myCost ; setCost(myCost) ; cout <<"the cost is"<< getCost() ; }
if I input 7.99 it returns 7.99, if I input 7.00 it returns 7 and not 7.00 as I would like. Why is that and how do I get around that...really don't have a clue sorry and can't think of anything...
thanks
You need to use the functions in iomanip. The decimals are there, they are just not being displayed.
So,
#include <iomanip> and see . You'll have to set the fixed setting first like they do in the example.
jonsca,
thanks for that. I had a read at the tutorial, not sure if I understand it correctly though especially when it comes down to distinguish between fixed and default...
this is what I came up with, and it works:
#include<iostream> #include <iomanip> using namespace std; double cost; double getCost( ) { return cost ; } void setCost( double Cost ) { cost = Cost ; } int main() { double myCost = 0.0 ; cout << "What's the cost? "; cin >> myCost ; setCost(myCost) ; cout <<"the cost is"; cout<< fixed; cout<< setprecision (2)<< getCost() ; }
Just so I understand this properly:
cout<< fixed;//not sure what it does
cout<< setprecision (2)<< getCost() ;
This instead effectively says that I want the floating number to display 2 digits after the period..is it correct?
I think what you're doing is correct, but:
Why dont you use 'printf ()'. This function is much handier, and lets you input everything you want (and print every way you want it).
Like this:
int main () { int foo = 5; double bar = 7.22, bar2 = 3.93; char ret = 'x'; printf ("This is my int 'foo': %d, these are my doubles 'bar' and 'bar2': %.0f and %.2f, and this is my 'ret' charachter : %c", foo, bar, bar2, ret); }
Try it!
Cheers
And, in the above, look at the doubles. First I print them with 0 precision, and the next one with 2 presicion.
(Output:
This is my int 'foo': 5, these are my doubles 'bar' and 'bar2': 7 and 3.93, and this is my 'ret' charachter : x
)
Cheers
jonsca,
thanks for that. I had a read at the tutorial, not sure if I understand it correctly though especially when it comes down to distinguish between fixed and default...
From that same site fixed means that: "the value is represented with exactly as many digits in the fraction part as specified by the precision field and with no exponent part." (presumably meaning that the implementation will find the closest floating point number that carries that value to a certain number of digits, and will not use scientific notation)
vs.
Floating point is a way to increase precision at the expense of the size of the number and vice versa. That is the default for cout.
I think what you're doing is correct, but:
Why dont you use 'printf ()'. This function is much handier, and lets you input everything you want (and print every way you want it).
This is probably one that could be argued either way. If the OP's class is using iostream, it's probably a good idea to stick with that.
Not to take this OT, but there are some interesting arguments about that here:
Hi thanks, well I don't use 'printf ()' because to be honest I have never come across it before...do you have any link where I can read a bit more about it?
It's a function carried through by the C standard library. See but read the examples first instead of the theory.
I wasn't endorsing your use of it, especially if your class is in C++. My google search was for arguments in favor of one way or the other and I included the link for completeness.
thanks guys. Jonsca sorry to labour the point but, to go back to the floating point issue, I had a look again at and the example there is:
// setprecision example #include <iostream> #include <iomanip> using namespace std; int main () { double f =3.14159; cout << setprecision (5) << f << endl; cout << setprecision (9) << f << endl; cout << fixed; cout << setprecision (5) << f << endl; cout << setprecision (9) << f << endl; return 0; }
which prints
3.1416
3.14159
3.14159
3.141590000
Now, the first cout is set to 5, so shouldn't the first result have 5 digits and be 3.14159? why is it rounding it? Same story for the second cout which is set to 9, so shouldn't the second result have 9 digits rather than 5? the "fixed" I think is clear enough.
I am finding myself in this situation at the moment. I have a program which takes 5 floating numbers as input from a file say 3.78, 6.658, 4.4569, 5.76549, 3.665439. I set
cout<<"numbers to be processed are: " <<fixed <<setprecision ( 6) <<numbers;// to indicate the numbers to be output
and with a for loop it prints all the above numbers. Obviously it displays:
3.780000
6.658000
4.456900
5.765490
3.665439
Any way to get the rid of the zeros but at the same time making sure that the last number prints all the digits after the period? I tried without using the setprecision function but what happens is that the last number is printed as 3.66544 and not 3.665439...
thanks
As far as the second 3.14159 (with setprecision at 9), the mode is still the default one, so the extra zeros are not displayed (from the cplusplus.com site
"On the default floating-point notation, the precision field specifies the maximum number of meaningful digits to display in total counting both those before and those after the decimal point. Notice that it is not a minimum and therefore it does not pad the displayed number with trailing zeros if the number can be displayed with less digits than the precision." ()
In terms of your request, what is your objective? (it seems to be changing from your original request) You could selectively format the number based on the digits after the decimal point, but that would get tedious. You are asking to have the default setting on some and the fixed setting on others. Perhaps if we knew what you were trying to accomplish...
Edited by jonsca: n/a
sorry didn't mean to be confusing. My original request and this one are in fact the same pretty much, it's just the examples I used that are different. I fully understand now my own example (the one with the cost function) and the next example was just to confirm that I understand how to deal with this precision business.
I have few numbers the program takes from a file, and they are:
3.78
6.658
4.4569
5.76549
3.665439
The problem I was having is when I cout them. With no precision set, the screen outputs this:
3.78
6.658
4.4569
5.76549
3.66544
rounding the 6th digit after the period in the last number.
With the fixed precision set to 6
cout<<fixed<<setprecision (6)...;
it displays
3.780000
6.658000
4.456900
5.765490
3.665439
which is what i expected but the trailing zeroe are a bit annoying so I was trying to find a way to get the rid of them. So reading the tutorial and your post I now know that the one to use is the default setprecision, so
cout<<setprecision (7)...;
because the default one takes into consideration numbers before and after the period and since 3.665439 is 7 digit I need 7. With this my output is sorted:
3.78
6.658
4.4569
5.76549
3.665439
What's annoying though, is that you need to know how many digits your numbers are before setting the precision up. So say that I take the input from a user and not from a file and the user inputs a number like 3.5645342314569 there will be no way that the number input can be displayed in full unless I set the (default) precision to be 14 in my program that attempts to display ... | https://www.daniweb.com/programming/software-development/threads/326577/floating-point-type | CC-MAIN-2018-05 | refinedweb | 1,721 | 81.73 |
The TypeScript team have released version 3.1 of TypeScript, following the recent 3.0 announcement, adding mappable tuple and array types and several other refinements.
Nearly every JavaScript application needs to map over values in a list, which is a pattern that gets simplified with ES2015 via rest parameters.
A common example provided by the TypeScript team:
function stringifyAll(...elements) { return elements.map(x => String(x)); }
Per the TypeScript release blog:
The
stringifyAllfunction>;
With this example, the function accepts an arbitrary number of elements and will return an array of strings, but type information about the number of elements would be lost. Previously the solution would be to overload function definitions, which quickly becomes inconvenient:
declare function stringifyAll(...elements: []): string[]; declare function stringifyAll(...elements: [unknown]): [string]; // ... etc.
TypeScript already introduced a mapped object type in a previous release, but this did not work as expected with tuple and array types. The change with this release is that this approach now works as expected rather than throwing cryptic error messages.
Per the TypeScript release blog:.
The other significant addition to the 3.1 release is ease of specifying properties on function declarations. React users are familiar with this as defaultProps.
As functions are just objects in JavaScript, it is easy to add properties to a function. TypeScript's original solution to this problem was namespaces, but this has introduced challenges when working with ES Modules, and do not merge with declarations made via
var,
let, or
const
For TypeScript 3.1, any function declaration or const declaration initialized with a function results in the type-checker analyzing the containing scope to track properties that get added.
Many other smaller changes and enhancements made the 3.1 release.
Beyond the 3.1 release, there are substantial improvements due in the TypeScript 3.2 release. The largest is Strict bind, call, and apply methods on functions, a complex enhancement the community requested nearly four years ago. This fix is yet another piece of the missing puzzle for variadic kinds, the most challenging collection of problems to solve to support the typing of higher-order functions. BigInt support is also part of the 3.2 release.
TypeScript is open source software available under the Apache 2 license. Contributions and feedback are encouraged via the TypeScript GitHub project.
Community comments
.
by Michael Robin /
.
by Michael Robin /
Your message is awaiting moderation. Thank you for participating in the discussion.
. | https://www.infoq.com/news/2018/10/typescript-mappable-tuple-array/ | CC-MAIN-2019-26 | refinedweb | 404 | 58.38 |
As of this writing, Open Event Server did not have the functionality to add, manipulate and delete checkout times of attendees. Event organizers should have access to log and update attendee checkout times. So it was decided to implement this functionality in the server. This boiled down to having an additional attribute checkout_times in the ticket holder model of the server.
So the first step was to add a string column named checkout_times in the ticket holder database model, since this was going to be a place for comma-separated values (CSV) of attendee checkout times. An additional boolean attribute named is_checked_out was also added to convey whether an attendee has checked out or not. After the addition of these attributes in the model, we saved the file and performed the required database migration:
To create the migration file for the above changes:
$ python manage.py db migrate
To upgrade the database instance:
$ python manage.py db upgrade
Once the migration was done, the API schema file was modified accordingly:
class AttendeeSchemaPublic(SoftDeletionSchema): """ Api schema for Ticket Holder Model """ … checkout_times = fields.Str(allow_none=True) # ← is_checked_out = fields.Boolean() # ← …
After the schema change, the attendees API file had to have code to incorporate these new fields. The way it works is that when we receive an update request on the server, we add the current time in the checkout times CSV to indicate a checkout time, so the checkout times field is essentially read-only:
from datetime import datetime ... class AttendeeDetail(ResourceDetail): def before_update_object(self, obj, data, kwargs): … if 'is_checked_out' in data and data['is_checked_out']: ... else: if obj.checkout_times and data['checkout_times'] not in \ obj.checkout_times.split(","): data['checkout_times'] = '{},{},{}'.format( obj.checkout_times, data['checkout_times'], datetime.utcnow())
This completes the implementation of checkout times, so now organizers can process attendee checkouts on the server with ease.
Resources
- SQLAlchemy Docs:
- Alembic Docs: | https://blog.fossasia.org/implementing-checkout-times-for-attendees-on-open-event-server/ | CC-MAIN-2022-21 | refinedweb | 308 | 55.24 |
08 December 2008 17:44 [Source: ICIS news]
By Nigel Davis
LONDON (ICIS news)--CEO Andrew Liveris last week promised a revised cost structure for Dow Chemical as it responded to new realities but the extent of the cutback was not clear.
Yet Liveris has long talked of a “transformation” for the largest ?xml:namespace>
Dow’s recent aim has been to lighten the asset footprint to get away from cyclicality and to focus more on important end-use markets. A company that is much closer to important industries and distanced from the oil barrel can, on the one hand, hope to grow faster and, on the other, avoid the worst of upstream (petro) chemical uncertainties.
In creating K-Dow with
K-Dow will run a sizeable chunk of Dow’s upstream petrochemicals and plastics portfolio. And it can be seen now that Dow’s structure will effectively be re-written when the K-Dow asset light venture is up and running and the Rohm and Haas acquisition fully absorbed.
Dow says it will significantly cut back on shared services and on the corporate centre as it changes. The corporate realignment will, in Dow’s words, “accelerate the company’s ability to shed high-cost assets and centralised functional structures”.
Dow is going to run three business models for the different parts of its business: joint ventures; the agriculture, health and performance products operations; and an advanced materials and market-facing group.
By doing that it sees an opportunity to cut out high cost plants – 20 in total it says now – and eliminate 5,000 full-time jobs, or 11% of it global workforce. These are sizeable cutbacks which are being made in addition to the temporary idling of some 180 plants worldwide and the cutting of 6,000 contractor jobs.
Dow has always been run lean, but these cuts represent a further significant step in the quest for real efficiency and cost effectiveness.
Savings of $700m (€553m) a year are expected by 2010 from these cutbacks. They can be made in addition to the anticipated Rohm and Haas acquisition cost savings of $800m a year, which are said to be achievable in the same timeframe.
Dow will need the savings in the short as well as the longer term. Current business can be little short of dreadful given the sharp slowdown in the key automobile and construction markets.
The recession in the
Not much can be expected in the way of a recovery in the first half of 2009, at least.
The poor outlook for US chemicals was highlighted last week when the American Chemistry Council’s chief economist, Kevin Swift, suggested that US chemicals output could fall by more than 5% next year amid a significant global slowdown.
Dow is being transformed but management is also reacting to events. “Today’s restructuring is designed to support the Dow of tomorrow. However, we are accelerating the implementation of these measures as the current world economy has deteriorated sharply, and we must adjust ourselves to the severity of this downturn,” Liveris said in a prepared statement.
“Transformation, by definition, requires a commitment to working differently,” he added. “We are moving from a highly centralised and standardised approach, to operating three very different business models with a lean and efficient c
The cutbacks linked to the new business structures will largely be made in support services with some jobs going at the corporate centre.
Some 2,000 jobs will transfer with the sale of businesses currently in the Dow Portfolio Optimization group, which back in February included film products, synthetic rubber and speciality copolymers, among other businesses.
In the face of the downturn Dow has idled 30% of its production capacity. And, for the past three months, according to Liveris, has been working on “code red”.
The entire industrial supply chain outside food and health is in a recessionary mode, he said on Monday.
The strategically oriented cutbacks will go some way to help the company preserve cash but management also wants to cut the cash requirement in 2009 by as much as $2.5bn.
It will do that through reduced working capital, given expected lower feedstock and energy costs, lower capital spending and some restructuring.
( | http://www.icis.com/Articles/2008/12/08/9177691/insight-dow-brings-forward-cutbacks-as-downturn-bites.html | CC-MAIN-2015-11 | refinedweb | 705 | 55.98 |
Question: For a random sample of returns audited by the IRS
For a random sample of returns audited by the IRS, the data in file XR13041 describe the results according to the income category of the audited party (coded as 1 – low, 2 = medium, 3 = moderate, and 4 = high) and the type of IRS personnel who examined the return (coded as 1 = revenue agent, 2 = tax auditor, and 3 = service center). At the 0.05 level, are we able to conclude that the category of return is independent of the type of IRS examiner to which a return was assigned?
A computer and statistical software.
View Solution:
A computer and statistical software.
View Solution:
Answer to relevant QuestionsFor ...It has been reported that 18.3% of all U.S. households were heated by electricity in 1980, compared to 27.4% in 1995 and 31.5% in 2005. At the 0.05 level, and assuming a sample size of 1000 U.S. households for each year, ...A pharmaceutical company has specified that the variation in the quantity of active ingredient in its leading prescription medication must be such that the population standard deviation must be no more than 1.20 micrograms. ...Given the information in Exercise 13.62 and data file XR13062, determine the 98% confidence interval for the population variance of the cooked weights for hamburgers prepared using the consultant’s recommended cooking ...Twenty-five percent of the employees of a large firm have been with the firm less than 10 years, 40% have been with the firm for 10 to 20 years, and 35% have been with the firm for more than 20 years. Management claims to ...
Post your question | http://www.solutioninn.com/for-a-random-sample-of-returns-audited-by-the-irs | CC-MAIN-2017-26 | refinedweb | 281 | 57.77 |
How to Add a Copy to Clipboard Button Using JavaScript
May 6th, 2022
What You Will Learn in This Tutorial
How to create a function which receives a string of text to copy to the users clipboard when called. a Joystick component
In the app we just created, an example page component that's already wired up to our router was created for us at
/ui/pages/index/index.js. To get started, we're going to open this file up and replace its contents with a skeleton component that we'll build our copy to clipboard functionality on:
/ui/pages/index/index.js
import ui from '@joystick.js/ui'; const Index = ui.component({ render: () => { return ` <div> </div> `; }, }); export default Index;
Here, we begin by importing the
ui object from the
@joystick.js/ui package: the UI framework portion of CheatCode's Joystick framework. Next, we create a variable
const Index and assign it to a call to
ui.component(). This method creates a new Joystick component for us using the options we pass to it as an object.
New to Joystick or never heard of it? Get a crash course on building your UI with @joystick.js/ui in this tutorial.
On that object, we've added a single property
render which is assigned to a function returning the HTML we want to render on screen when we load this component in our app. For now, we're just returning a string with an empty
<div></div> tag.
/ui/pages/index/index.js
import ui from '@joystick.js/ui'; const Index = ui.component({ css: ` div { display: flex; } div button { margin-left: 10px; } `, render: () => { return ` <div> <input type="text" /> <button class="copy">Copy</button> </div> `; }, }); export default Index;
Building out the HTML, next, we want to add an
<input /> tag with a
type of
text and a button with a
class of
copy. Our goal will be to take whatever we type into the input and when we click the "Copy" button, copy it to the clipboard. Just above this, we've added some simple CSS to clean up the display of our input and button so they sit next to each other on screen.
Adding a copy to clipboard
Next, we need to wire up the button that will handle the copy of our text to the clipboard.
/ui/pages/index/index.js
import ui from '@joystick.js/ui'; const Index = ui.component({ events: { 'click .copy': (event, component) => { const input = component.DOMNode.querySelector('input'); component.methods.copyToClipboard(input.value); }, }, css: `...`, render: () => { return ` <div> <input type="text" /> <button class="copy">Copy</button> </div> `; }, }); export default Index;
In order to handle the copy event, we need to add an event listener on our button so that when it's clicked, we can get the current input value and then hand it off to our copy function.
Here, we're adding an option to our component
events which is assigned to an object where each property name is the combination of a type of DOM event we want to listen for and the element we want to listen for it on
<event> <element>. To that property, we assign a function that we want Joystick to call whenever that event is detected on that element.
For our needs, we want to get the current value of the
<input /> tag we're rendering down in our HTML. To do it, we anticipate that Joystick will pass us the raw DOM event that's taking place as the first argument to our function, and as the second argument, the current component instance.
On that instance, Joystick gives us access to the current component as it's rendered in the browser at
component.DOMNode. This is a plain, JavaScript DOM node object, which means that we can perform any standard JavaScript methods on it. Here, we're calling to
querySelector() to say "within this element—
component.DOMNode—look for an element called
input."
With that element, next, we call to
component.methods.copyToClipboard() passing in the
value property of our
input (this will contain the text value currently in the input).
Our last step is to wire up that
methods.copyToClipboard() function to make this work.
/ui/pages/index/index.js
import ui from '@joystick.js/ui'; const Index = ui.component({ methods: { copyToClipboard: (text = '') => { const textarea = document.createElement("textarea"); textarea.value = text; document.body.appendChild(textarea); textarea.select(); document.execCommand("copy"); document.body.removeChild(textarea); }, }, events: { 'click .copy': (event, component) => { const input = component.DOMNode.querySelector('input'); component.methods.copyToClipboard(input.value); }, }, css: `...`, render: () => { return ` <div> <input type="text" /> <button class="copy">Copy</button> </div> `; }, }); export default Index;
This is the important part. On a Joystick component, we can define arbitrary functions we want available under the
methods object. Here, we've added
copyToClipboard() as one of those methods ("method" is just the proper name for a function defined on an object in JavaScript), taking in a string of
text (here, the value we just pulled from our input, but potentially any string we want to copy to the clipboard).
Because JavaScript lacks a native "copy to clipboard" feature, in order to make this work, we need to do a slight hack.
Inside of this function, first we want to dynamically create a
<textarea></textarea> element in memory. Next, we assign the value of that
textarea element to the
text we passed into
copyToClipboard(). Once this is set, we dynamically append the
textarea to the
<body></body> tag of our browser and then immediately call the
.select() method on it.
Note: the
document.execCommand()function is listed as being deprecated, however, has well-established support across browsers. The deprecation status is due to an inconsistent implementation across major browsers which is deemed as the rational for flagging it as deprecated. It still works for our needs—and browsers have kept it implemented due to its wide usage—so while you shouldn't worry immediately, make sure it works at the time you read this. You can learn more about the deprecation status in this StackOverflow post.
Next, we use the
document.execCommand() function passing the string
"copy" to tell the browser to perform the copy command which will copy whatever is currently selected in the browser to the clipboard. Finally, we call to
document.body.removeChild(textarea) to remove the
<textarea></textarea> we just injected.
That's it! Now, if we open up our app in the browser at
when we click our button the current value of our input will be passed to
methods.copyToClipboard() and automatically be copied to the clipboard.
Wrapping Up
In this tutorial, we learned how to create a simple function for copying text to the clipboard. We learned about wiring up a simple UI component using Joystick and then, when clicking a button, copying the current text of an input to the clipboard.
Get the latest free JavaScript and Node.js tutorials, course announcements, and updates from CheatCode in your inbox.
No spam. Just new tutorials, course announcements, and updates from CheatCode. | https://cheatcode.co/tutorials/how-to-add-a-copy-to-clipboard-button-using-javascript | CC-MAIN-2022-21 | refinedweb | 1,171 | 55.44 |
Agenda
See also: IRC log
<scribe> scribe: Gregory_Rosmaita
<scribe> ScribeNick: oedipus
<Steven> code is CONF4
<Steven> 26634
<Roland>
4 XHTML2 items: the P content model, Navigation (nl in or out?), Semantics and Elements versus Attributes, how to incorportate ITS
RM: start with news from the A.C. meeting once reach critical mass
SP: would very much like to report, but want shane and mark to be here when i do
RM: brief update on PER
MG: Shane said he'd be late yesterday
scribe's note: [steven ping outliers]
minutes from last regularly scheduled meeting:
RM: brief update with PER?
SP: didn't make friday deadline due to AC meetings; have to get fiinished; still moritorium this week on publishing due to AC meeting, should be published next week, if all goes according to plan
RM: just matter of questoinnaires?
SP: PER has to be voted upon; extra administrivia - creating detailed questionnaires with pointers (creating now - have to go out simultaneously with PER anouncement)
RM: that's all we need do?
SP: yes
RM: any other administrivia?
scribe's note: deafining silence
GJR: in response to feedback and discussion at last virtual f2f i have updated the "for" attribute proposal
GJR: changes: proposed for Text Attributes collection, not Core collection
1. That the for/id mechanism, which is already broadly supported in user agents and assistive technologies, be repurposed and extended in XHTML2 to provide explicit bindings between labelling text and the object or objects that text labels;
2. That the for/id mechanism serve as a means of re-using values for: ABBR, D (the single letter "dialogue" element), DFN;
3. That the for/id mechanism serve as a means of binding a quotation, contained in the Q element, and a corresponding CITE declaration which identifies the source of the quote;
4. That the for/id mechanism serve as a means of marking text which has been inserted, contained in an INS, and that which it is intended to replace, contained in a DEL tag, as illustrated below;
SP: much of AC meeting, but not
all, in sphere of HTML5 and XHTML2
... started monday morning with panel - XHTML2 side represented by myself and ben adida (made cross-continental day trip); neutral people: Larry McMaster from Adobe; and HTML5 people represented mainly by David Baron
... nothing much to report about it; Hegeret was chair; put questions to panel; people in audience put questions as well -- no demos, just Q&A
RM: link to AC minutes?
<Steven>
SP: Chaals McN web standards
oriented; Larry MM neutral; Sam Ruby co-chair of HTML WG; David
Baron works for Mozilla, very much HTML5er; Henry Thompson, Ben
Adida and myself (Steven Pemberton)
... at least 2 negative comments from audience: Daniel Glazman (not there physically but on IRC) - very anti-XHTML2
... Arun (represents mozilla) - need to ask why against XHTML2 in W3C? don't think mozilla is anti-XHTML2, but hard to separate personal opinions from corporate agendas; aim is to close down XHTML2
... good feedback after panel; lots of red herrings being spread in discussion; tried to expose falicies
... after that meeting had breakout groups - about 20 in XHTML2 breakout group
... not minuted in IRC, hand-made minutes - trying to find if up in w3c space yet
... 2 breakout groups: 1st day: discuss issues (extended panel) - on second day, discussion on what to do with situation
... second breakout more interesting; discussion unencumbered by knowledge of what XHTML2 is all about; Raman and Charlie Wiecha of IBM knes about XHTML2, but rest of participants very shallow knowledge
... asked who is using 2 technologies; one person said, "since HTML5 seeks to make all pages conformant to HTML5, HTML5 is what people use
... explained modularization and the packaging of modules to create XHTML2
... because our charter has always been modularization, modules are deliverables; XHTML2 is a collectoin
... Arun surprised that there are big companies using XHTML and XForms
... meeting concluded with agreement that Sam Ruby and Steven Pemberton should work on merging HTML5 and XHTML2
... made it very clear in meeting that these aren't 2 slightly different markup languages, because underlying MVC architecture in XHTML2, that is laacking in HTMl5; would have to get HTML5 WG to accept that architecture so 2 can be merged
... if choice between merging and not merging, think should keep separate unless agree to accept XForms and extensibility
... SamR and i can discuss to ascertain options
... in conclusion, think that we are now in stronger position
... 2 things can happen: HTML5 people reject collaboration or we do merge and HTML5 people required to take our approaches on board (m12n, MVC, etc.)
... either of those 2 choices much better than shutting down XHTML2
... SamRuby is new co-chair of HTML5 - very positive interaction with him
... Sam Ruby wants to work together, but a lot of work to herd that enourmous herd of cats in HTML WG
... doubt that core HTML5 people will accept collaboration
GJR: did sam mention the initative at mozilla to produce a rival spec to HTML5?
RM: take more stable to have
third version of HTML5
... pragmatic - how to achieve a deliverable
SP: wasn't mentioned
<Tina> Thank ye
GJR: previous pointers: Rob Sayre of IBM is producing a new draft which is hixie's draft minus new inventions plus all the stuff that was removed
RM: will be taking features from HTML5 spec and adding them on; means of incrementally deploying HTML5
<Steven>
GJR: being deployed by fiat now
SM: more socially acceptable
RM: extensibility already being done by implementation by fiat of HTML5
SP: one discussion at AC meeting
in first day's breakout group was lack of extensibility
... consensus of breakout group was extensibility needs to be supported
... from POV of merging, extensibility essential
... long discussions about extensibility and what needs to be able to be done
SM: agreed upon definition of term "extensibility"?
SP: no definition or agreement on
what would fall under rubric of extensibility; put forward
strong view that people should be able to add own elements and
attributes in standard way to foster new forms; cited XBL as
example
... when i trace minutes for breakout groups will post link
GJR: from WAI/PF's point of view
extensibility and namespacing is essential, otherwise we will
end up with ARIA 1.0 hard coded into HTML5, but we are already
working on ARIA 2.0
... WAI/PF needs to retain control over ARIA's vocabulary and definitions
SP: some people surprised that
ARIA sprang from XHTML Role Module
... good to have BenA there on first day; Ben stated that it would be wrong to give XML serialization to a group of people who fundamentally oppose and disllike XML/XHTML
RM: return to this later - have a few comments
SP: worth watching discussion on AC forum; have to be on AC to contribute
GJR: one could always use www-archive for comments pointed at AC
SP: encouraged by meeting; interested in how the rest of the HTML WG responds to combining 2 groups
RM: should consider ramifications for XHTML
SP: LarryMM suggested i co-chair with Sam - not my idea of fun at the moment :-)
RM: first 2 topics also being worked on by HTML5
<Steven>
RM: HTML5 doing much of what we are doing with P - placing limitations on it
SP: pasted pointer to breakout session described above into IRC
<Steven>
SP: day 2 hasn't been posted yet - Sam Ruby making minutes
TH (from cited post): "I would argue that common concept of a paragraph is quite different
from that we currently use in the XHTML draft, and that we should
change it so that it reflect the way a paragraph is normally understood
by authors, namely the way it is currently defined in the XHTML 1.*
series languages."."
RM: P content model as defined in present draft cause anyone a problem
SP: background: when originally
designing text part of XHTML2, had a number of comments about
the P content model not matching what perception of P is
... P defined in HTML4x too simple - could not embed images or table in paragraph; request was for things embedded in P be part of content model
... current content model of P is an attempt to do that - represent as much as possible the context of the paragraph, but also attempt to avoid P nested in P - P nested in TABLE cannot have child."
<Steven> (PCDATA | Text | List | blockcode | blockquote | pre | table )*
GJR notes he has proposal to deprecate TABLE for layout/style as BLOCKQUOTE for that use was deprecated in HTML4x
SP: always been opinion of this
WG; don't explicitly say "deprecated", but agree that TABLEs
are TABLEs and stylesheets should be used for layout
... proposed TABLE role="presentation" doesn't undo the damage, in fact almost encourages it
GJR: strong agreement - wrong approach
AC: no presentation - OBJECT
should be used to embed video, audio, or presentation
... more like a user-modality for TABLE - agree with SP and GJR that layout tables should be banned
TH (from post) "But frankly I feel we have a problem. When humans communicate we do so by agreeing on the of words - and various other things outside the scope of this comment - so that when I say banana, you know its not an orange of which I speak."
tina?
<Tina> I am, but noise in office
tina, can you explain your proposed changes to P content model
<Tina> oedipus: certainly. We keep the one currently in use for HTML.
RM: would like more examples - if want P element with example and discussion of this issue - could do this way (compatible with past) or new way
SP: TH wants to exclude people who believe P is something different than what she is proposing
RM: irritating when have to
change prose into a list
... if write normal english: ingredients are: a) ; b) ; c);but cannot style as list because is prose list
... that is standard natural language usage
<Roland> ingredients are: a; b; c.
SP: including a list in P is perfectly valid
RM: examples would help
SP: opened a book "a case in point is blogs:" followed by list of 10 items; i content that in natural language usage that is a single paragraph, but HTML doesn't allow the list to be part of the P
GJR: agree - whether list is prose or formatted as list, belongs to the P and should be inside the P
<alessio> +1
<Tina> A suggestion, as quoted from me, above would be to allow lists - possibly inline lists - but exclude other use.
RM: alternative: leave as is, insert 2 examples, and note asking for feedback
ACTION - Gregory: draft example of P with prose list and structural list
<trackbot> Sorry, couldn't find user - -
<scribe> ACTION: Gregory - draft example of P with prose list and structural list [recorded in]
<trackbot> Created ACTION-65 - - draft example of P with prose list and structural list [on Gregory Rosmaita - due 2009-04-02].
tina, could you provide examples of other uses of P?
or a list of what you would exclude from the P content model?
<Tina> No, I don't see any reason to continue the discussion, in particular if we are speaking merging the two WGs - HTML 5 design principles, if memory serve, insist on backward compatibility. Until it decided whether to merge or not the discussion is moot.
RM: only one causing difficulty
with P content model is TABLE
... list, blockquote, pre and table
<Steven> (PCDATA | Text | List | blockcode | blockquote | pre | table )*
GJR: why blockquote and not blockcode?
SP: blockcode is part of content model
RM: what is normative? DTD or spec?
SM: spec always wins
RM: where spec doesn't include blockcode, bug in DTD
SM: no DTD for XHTML2
SP: not from DTD but modulariztion code
RM: still looking at what we
pointed to originally
... list, blockquote, pre and TABLE
SP: english text is wrong -
should also include blockcode
... module text at top is definitive version
RESOLUTION: fix XHTML2 prose to include blockcode
SM: shouldn't be in text
SP: plus 1 to that
GJR: following wiser heads like a lemming
SM: no other element describes content model in prose
SP: point of english text is to explain diff between XHTML2's P and earlier versions
RM: simple link-back to definition would help
SP: need to get that automated by
shane
... spec written as small files - by element or attribute, which then get put together in standard way
<ShaneM> It should read: In comparison with earlier versions of HTML, where a paragraph could only contain inline text, XHTML2's paragraphs represent a richer content model more consistent with the concept of a paragraph.
GJR: plus 1 to shane's proposal
RM: talk about attributes, but not content model
SM: talk about content model
elsewhere - may need to reinforce in this module because so
large
... proposed text
SP: is example of P with embedded UL in it
RM: in contrast to what was done in previous versions P /P UL /UL rather than P UL /UL /P
SM: mistake for us to include references as to how things used to be
RM: alternative today - P can contain lists; put side-by-side explaining can do either of these
SM: ok
proposed RESOLUTION: "In comparison with earlier versions of HTML, where a paragraph could only contain inline text, XHTML2's paragraphs represent a richer content model more consistent with the concept of a paragraph"
RM: not sure need "more consistent" clause
proposed RESOLUTION: "In comparison with earlier versions of HTML, where a paragraph could only contain inline text, XHTML2's paragraphs represent a richer content model consistent with the concept of a paragraph"
RM: richer content model of paragraph should be sufficient
proposed RESOLUTION: "In comparison with earlier versions of HTML, where a paragraph could only contain inline text, XHTML2's paragraphs represent a richer content model.
RESOLUTION: replace current explanation of P content model with "In comparison with earlier versions of HTML, where a paragraph could only contain inline text, XHTML2's paragraphs represent a richer content model."
TEN MINUTE BREAK - RECONVENE AT HALF-PAST HOUR
question: Do we really need four different types of lists in XHTML 2.0?
<Tina> oedipus: an exaggeration, surely.
<Tina> My 2 whatsits: yes. We DO need a rich set of lists for various structures that needs to be marked up. I would propose we add an inline-list to the ones we have, plus, of course, a 'menu' or 'navigation'
current editor's draft definition of NL:
RM: do we need 4 kinds of
list?
... discussed - fairly broad concept; item about elements versus attributes topic is related
... why did we create NL?
SP: in early days, 1 thing we did
was observe web sites to identify things on web sites that
represented concepts not represented in common HTML
markup
... one thing that we concluded was types of list purely for navigational purposes - semantic advantage (expecially from A11y POV) advantageous; developed before developed Role and RDFa
... new markup allows NL without new type of element]
... instead of NL, UL role="navigation"
RM: device independence group worked on this; large areas of page - are areas devoted to navigation
<Tina> OL, not UL. This is still a rather dramatic conceptual change. Why would we want to do that - and, on the flipside, not then simply have ONE list?
RM: not catered for inside
markup; navigation is important property
... difference from my POV is navigation is more than list
... HTML5 has NAVIGATION element - useful notion: can be more to navigation than items; headings (primary navigation, secondary navigation)
... would like to reframe converstation from NL to NAVIGATION section
<Roland> HTML5 :
<ShaneM> I agree with Steven that @role can be used to indicate that a section is related to navigation.
RM: felt navigation was structure
<ShaneM> <section role="navigation">...</section>
SP: use SECTION role="navigation"
is equivalent
... could also use UL role="navigation" or OL role="navigation"
... can be done by attaching role to SECTION or directly to list
<Tina> Have we agreed to leave *all* semantics to RDFa and @role?
<ShaneM> Tina: No, I don't think so.
RM: OL role="navigation" equals SECTION role="navigation"
SP: MarkB would say NL wrong because makes list with specific semantic meaning; sturcture is ordered list and structure is navigation; if want section on navigation, use SECTION role="navigation"
<Tina> ShaneM: that begs the question - which semantics do we leave to elements? We already have three different list types. If they are there for structure only, then why don't we simplify and make one?
SM: context - state of art when
introduced NL in visual user agent wasn't possible without
heavy scripting; but today, that can be achieved with CSS
... throw out NL
SP: can live with that
AC: me too
GJR: me too
<mgylling> +1
<ShaneM> Note that @role already has a predefined value for "navigation"
RM: would prefer a NAV element
rather than just list
... no element whose specific role is navigation, can be satisfied by assigning role to other structural elements
SP: kept a lot of elements that aren't strictly necessary because of use-and-practice with list
SM: extended content model for DL
by adding DI
... very positive move
... can't decide if TH making serious point or playing devil's advocate
... appreciate that there is a significant presentational and semantic difference between OL, UL, and DL - DT and DD need to be grouped in order to make sense
... don't think a lot of value removing things people are already familiar with
.
SM: does beg the question: "does it make sense for us to do things in language that we know will not work right in existing UAs?"
RM: not on agenda, but could
discuss when return to HTML5 discussion
... making incremental changes that make it hard to deploy - is it worth return on investment
... do we need to introduce DI type of thing to discuss later
... concrete example?
<Tina> Since we are already changing or removing things people are already familiar with. Consistency is key.
SP: resolution to remove NL?
proposed RESOLUTION: remove NL from XHTML2's List Module
RM: propose we remove NL
<Steven> and replace with use of @role="navigation"
GJR: plus 1 with SP's caveat
<Steven> as necessary
SM: we created "navigation" role
proposed RESOLUTION: remove NL from XHTML2's List Module and replace with use of role="navigation"
SP: current model for DL wouldn't break existing user agents
<Steven> I think
GJR: agree with SP - will make DL stronger and more useful
<Steven> +1
<Steven> on resolution
<mgylling> +1
proposed RESOLUTION: remove NL from XHTML2's List Module and replace with use of role="navigation"
plus 1
<ShaneM> Tina: I think there is a (new) trend toward NOT removing things that people are familiar with.
<ShaneM> oops...
definition of navigation from vocab document: "navigation indicates a collection of items suitable for navigating the document or related documents."
RM: seem to have gotten a bit
mixed up - talking about multiple things
... resolution to remove NL
proposed RESOLUTION: remove NL from XHTML2's List Module and replace with use of role="navigation"
<ShaneM> +1
<Roland> +1
<Steven> +1
<alessio> +1
RESOLUTION: remove NL from XHTML2's List Module and replace with use of role="navigation"
<ShaneM> ACTION: Shane to remove the nl element from XHTML 2 [recorded in]
<trackbot> Created ACTION-66 - Remove the nl element from XHTML 2 [on Shane McCarron - due 2009-04-02].
SM: one related item is DL
SP: changes won't change deployment
SM: DI would be ignored?
MG: DI is optional
GJR: provides nice low-grade binding for DDs
RM: DI introduced to solve what particular problem?
)."
<mgylling> ... di solves a problem that could also be solved with @for...
SP: if 2 things are related, DI can express that; presentation: hard to put border around DT and DD; from semantic POV want them to be joined at head and not hip
markus, do you have more to say on "for"
RM: like paragraph - if don't want to use DI, don't have to
<mgylling> no - I am all for DI.
good
RM: any other potential pitfalls with lists?
SM: added in list module the caption element and hooked into content model for all lists
<ShaneM>
RM: lists allow caption
GJR: might want to consider LEGEND
<Steven> We need to consider the purposes of LEGEND LABEL and CAPTION
<Steven> and work out whether to merge
<alessio> yes, it's a very good point
SM: haven't addressed use of XForms inline content with other forms of inline content
Use of FIGURE, LEGEND, and @alt
Three Stages of A Butterfly's Life Example:
<FIGURE aria-
<LEGEND id="l1">The Three Stages of a Butterfly's Life Cycle</LEGEND>
<IMG alt="Stage 1: The larval stage." src="butterfly1.svg"
longdesc="butterfly1.html">
<IMG alt="Stage 2: The pupal stage." src="butterfly2.svg"
longdesc="butterfly2.html">
<IMG alt="Stage 3: The adult stage." src="butterfly3.svg"
longdesc="butterfly3.html">
</FIGURE>
a) each individual image's short alternative text;
b) the grouping to which the image belongs (if it is one of a series presented in a FIGURE) or any other modality-specific content contained in HTML5's media-specific elements, including AUDIO, VIDEO, OBJECT and CANVAS;
RM: need to orient readers and contextualize use of XHTML2 to alter content and improve usability of content - how to pull pieces of m12n together
GJR: i will send "thoughts on LEGEND" used in PF deliberations over terse descriptors in HTML5 to XHTML2 list
RM: like examples - pick up as a
template and build upon it
... christina once worked on something similar, but we haven't undertaken anything as a WG
SP: no, we haven't really
RM: continuing developing document, steven?
SP: received a lot of input at AC meeting on how should be structured
SM: does anyone understand the ITS question?
SP: background: googletranslate -
when automatically translates page, ITS helps markup page to
assist process; when i say "window" don't translate because is
technical term;
... semantic markup with specific domain: meaning of words with respect to other languages
<mgylling>
RM: who is driving this request
SP: i18n
<Steven> Then from there, run batch file <cmd
<Steven> its:Build.bat</cmd>.</p>
MG: investigated ITS - 3 options
to introduce rules into document - inline (similar to @style),
xlink to external document, or put info in HEAD
... not just question of attribute, but should we support XLINK in HEAD, etc.
RM: can link to ITS definition, full stop
SM: not an option
SP: wouldn't let us do that?
SM: our architecture doesn't
allow for arbitrary content models; need to specificy what goes
where
... ITS was on rec track; asked us to do LC review; we said fine, but forgot M12n; listened to us and produced modules and went to REC
... should we incorporate into XHTML 1.2 - no, but i was given action item to put into XHTML2 - too many options, need to pick one
... should ask ITS WG how to use ITS in our module
RM: ITS WG closed
... ITS interest group still active
... should ping them to ask "how do you think this applies to us?"
SP: created something similar to
CSS - create rules in HEAD or inline
... a lot of their stuff we have anyway - don't need @dir because took from us and put in their namespace
GJR: notes that this is a good trend - similar to timesheets
SP: translate rules - include their rules into HEAD and then in BODY only thing that is left is translate equals yes or no
MG: correct; have schema modules
for ITS we can import
... external sheets via XLink
... should ask if can use LINK element instead
RM: sounds reasonable
SP: invite someone from ITS to join us on a call to discuss
GJR: sounds reasonable
SP: should be able to find someone courtesy of RichardI
<scribe> ACTION: Steven - talk to Richard to ask if someone from ITS can join an XHTML2 call to discuss this further [recorded in]
<trackbot> Created ACTION-67 - - talk to Richard to ask if someone from ITS can join an XHTML2 call to discuss this further [on Steven Pemberton - due 2009-04-02].
RM: is anyone recognizing ITS?
SP: if no one is producing content with it answer is no
RM: are we the best people to bootstrap this?
SM: should be bending over backwards to reuse W3C technologies and standards
GJR: first principle of WCAG - if pertinent technology exists (such as MathML) use it
<Steven> r12a suggests 10 01yves savourel 01chair of the former WG
RM: doesn't sound too onerous
<Steven> and cc to Felix of W3C
RM: don't need its prefix, just "yes" or "no"
SM: does spec allow chameleon?
MG: published note on how to incorporate ITS into XHTML family
<Steven> ysavourel at translate.com
processing expections for ITS:
<Roland>
."
MG: roland's pointer the one i was thinking about
SM: last one GJR put in is what i was looking at
RM: XHTML M12n 1.1 -
SM: our treatment of schema allows us to bring in elements and attributes from other namespaces; don't have to include in our namespace if already exists elsewhere and is in use
"1) ITS and TEI: ITS rules is allowed to appear in the TEI metadata section (the teiHeader). The local ITS attributes are added to the global attribute set for all elements. ITS span is added to the content pattern model.common (most inline contexts)."
)."
SP: reading from spec: "one way to associate document with external ITS rules is to use optional XLINK"
<Steven> so it sounds optional
SM: questions we have: don't
support XLink, so can we use LINK? leave in ITS space and use
their suggested model?
... inclination is to invite someone to discuss XLink - for content model, take what proposed for XHTML 1.1 leave in ITS namespace and do what they said
proposed RESOLVED: XHTML2 WG will discuss ITS integration and use of LINK versus XLink with representative from i18n
RESOLUTION: XHTML2 WG will discuss ITS integration and use of LINK versus XLink with representative from i18n
SP: already invited them
SM: thank you
RM: anything else on ITS?
RM: quantity values question
SP: when we have href type and
src type which allows one to define what values are suitable;
in HTML4 have type on HREF - comment that says what is on other
end - just a claim, not firm basis for content
negotiation
... in XHTML2 have list of types used for content negotiation
... comment that don't take into account QValues
... been boning up on QValues
RM: should add to tracker
SP: if say "here is an image" may
be in 10 diff formats, but want SVG or PNG to be first choice,
if user agent can't handle SVG or PNG, have to provide
something UA says can accept
... answer may be no qvalues in source
SM: think that is the
answer
... QValue responsibility of UA; intersection of what UA can handle and what author can offer
SP: order of things in
specification important - take first or highest q?
... when UA specifies what is willing to accept does it mean willing to accept them equally
SM: have to check HTTP spec
... order is probably significant - will check
<Steven> ACTION: Steven to work out how to merge q values in the specification of content negotiation with hreftype etc. [recorded in]
<trackbot> Created ACTION-68 - Work out how to merge q values in the specification of content negotiation with hreftype etc. [on Steven Pemberton - due 2009-04-02].;statetype=-1;upostype=-1;changetype=-1;restype=-1
RM: work through 16 open issues on shane's tracker?
SM: not now
RM: when?
SM: not sure what to do with 5 year old comments
RM: are any of the issues still
relevant?
... how to deal with them?
GJR: port them to W3C tracker and close those that are moot?
"QNames are the way that the working group, and indeed the W3C, handle having
data that comes from differing sources. The working group is not willing to
change course at this time
SM:;user=guest;statetype=-1;upostype=-1;changetype=-1;restype=-1 needs to be split up
SP: some just comments
... several of these things don't need to do
... can answer, but no action necessary
... real issues: keep BR (which i think we do)
SM: were instructed by TBL to keep BR
SP: a lot of editorial comments
<Tina> What is the structural purpose of BR? That should be the only reason why we keep it or toss it.
<Tina> Yes. What's our use case for keeping it?
SP: could say that WG received this remark and is not required to answer; get input from more recent suggestions
<Tina> Then I suggest we get rid of BR as more-or-less physical markup.
tina, do you want to work on a proposal to eliminate BR?
deprecate in favor of use of L ... /L
anne van k on L: "Didn't BLOCKCODE preserve whitespace by default? What do we need the L
element for here? And as mentioned before, BR is still needed. I also
think that a better use case for L should be presented, this one is bad."
<Tina> oedipus, I don't have the time to write up anything formal, I'm afraid.
me neither, but i might as well take a whack at it right now
GJR's take: BR is a presentational concept; to express that a line of content is intended to be interpreted as single line of content, authors should use the L element to mark the beginning and end of a line.
RM: keep differences from status-quo to a minimum - makes easier to deploy in existing browsers
<Tina> oedipus: I agree with that.
SM: "1.1.2. Backwards
compatibility
... will update as appropriate
... 1.1.2. Backwards compatibility
<Tina> We are already deviating from that, however, by changing content models. Removing presentational markup is surely a good idea.
SM: wants BR back; instructed to do it, but haven't done it
GJR's take: BR is a presentational concept; to express that a line of content is intended to be interpreted as single line of content, authors should use the L element to mark the beginning and end of a line.
SM: agree
RM: back to pragmatic - authors need to understand what to do - how much benefit from being purists, how much from being practical - can we live with either or
SP: can live with keeping it, but with a note stating that L is preferred method
<ShaneM> ACTION: Shane to put br element back into XHTML 2 with a note that there are better ways to mark up lines. [recorded in]
<trackbot> Created ACTION-69 - Put br element back into XHTML 2 with a note that there are better ways to mark up lines. [on Shane McCarron - due 2009-04-02].
proposed Resolution: restore BR
SP: objections?
GJR: object
SP: if objections, don't have resolution
RM: GJR, do you believe we should not do this?
GJR: willing to compromise on BR if we add note on use of L
<Tina> I see no good reason to put a presentational element back in. This isn't as much about pragmatic solutions - CSS can do the visual if need be.
GJR: is there any override mechanism for BR?
SP: compromise: include BR but mark as deprecated
GJR: yes
<ShaneM> deprecated? in a legacy br module?
proposed RESOLUTION: re-introduce BR, marking as deprecated, and point out that for accessibility, is much better to use L
<Steven> +1
<ShaneM> +1
GJR: plus 1
AC: yes
<Roland> +1
<mgylling> +1
<alessio> +1
RESOLUTION: re-introduce BR, marking as deprecated, and point out that for accessibility, is much better to use L
RM: next one is ADDRESS element
SM: request is make content model for address richer, or introduce a BLOCKADDRESS element
GJR: isn't this covered by role="contentinfo"
vocab doc: "
contentinfo has meta information about the content on the page or the page as a whole.
<Steven> By the way, there is a new rrsagent in the works:
SM: not inclined to change from block to inline or to add blockaddress
SP: non-structural element that
only adds semantic information
... semantic info is terribly vague - can't extract much sensible out of ADDRESS
RM: HTML5's ADDRESS is not block
SM: problem is content model restricted;
'The address element represents the contact information for the section it applies to. If it applies to the body element, then it instead applies to the document as a whole"
<Tina> That does appear fairly clear, if not detailed. What is the use case for changing it?
"The address element must not contain information other than contact information."
<ShaneM> Tina: the request is to make the content model richer
GJR: HTML5 Address is a child of FOOTER
<Tina> If so, do we need to change the element or simply add other elements which go inside it that allows an author to define up the various pieces?
GJR: address is part of FOOTER,
but restricted to contact info only
... in HTML5
<ShaneM> Tina: I think we just could make the content model richer.
Content model for FOOTER in HTML5: "Flow content, but with no heading content descendants, no sectioning content descendants, and no footer element descendants."
SM: either add blockaddress or
fix rich content model
... objections to making content model of ADDRESS richer?
... need to define "richer"
... same as SECTION
<Tina> ShaneM: not a bad idea. We can keep ADDRESS, then add various elements for marking up specific sections of contact info. Or rely on namespaces for people to use elements from other XMLs.
RM: why not say SECTION role="address"
SP: on other hand, could just say ADDRESS is shorthand for SECTION role="address"
RM: no difference in semantics
for ADDRESS and SECTION role="address"
... need to define semantics of ADDRESS
SM: DIV role="p" is not a
substitute for using P - if element has semantics, use the
element
... have ADDRESS element - could say "if need area of document with richer content model and address information, use SECTION role="address"
RM: no existing "address" role
GJR: when we did ARIA/HTML5 analysis decided that "contentinfo" more broad than HTML's ADDRESS
SM: defer to dublin core or VCard?
<Tina> Suggestion: keep <address> as is, and encourage authors to use other markup languages for the specifics.
SM: vocab collection for role is missing fundamental concepts - is that because we are deferring to DC
SP: do in RDFa instead of role
RM: on typical page, navigation area, content area, contact area very common - address related to contact info
SM: dublin core values we can use for that
RM: broke up page into appendix, content, copyright, etc.
SM: can add a role
<alessio> agree
RM: can state "not changed from HTML4; if want richer mechanism, create it according to the markup family's extension rules
SM: probably way to group all of
this together
... should we introduce additional role values
GJR: yes
SP: good point
GJR: would like to differentiate between explanatory note and referential note
SM: in existing vocabulary
from vocab document: note: "note indicates the content is parenthetic or ancillary to the main content of the resource."
GJR: there are 2 types of note: referential (citation, endnote) and annotative (what the vocab doc says)
SP: resolution?
<ShaneM> Tina: I think that is where we are ending up. Thanks!
RM: leave address as-is, if want to create richer structures for that information, use SECTION
proposed RESOLUTION: leave ADDRESS as-is, add note that if author wants to create richer structures for that information, author can do so following langauge's extension mechanism (e.g. use SECTION)
<alessio> +1
<ShaneM> +1
proposed RESOLVED: leave ADDRESS as-is, add note that if author wants to create richer structures for that information, author can do so following langauge's extension mechanism, e.g. use SECTION
<Roland> +1
RESOLUTION: leave ADDRESS as-is, add note that if author wants to create richer structures for that information, author can do so following langauge's extension mechanism, e.g. use SECTION
SM: need to discuss additional
role values - add to next f2f agenda
... heading element - "confusing" - example of use of both
... think addressed this by moving things around in document
... anne objects to P element content model that allows some block-level elements to be mixed in
GJR: reminder earlier RESOLUTION: replace current explanation of P content model with "In comparison with earlier versions of HTML, where a paragraph could only contain inline text, XHTML2's paragraphs represent a richer content model."
SM: PRE element comments
... changed example
GJR: PRE is a problem for accessibility
RM: editorial comment
SM: separator element -
SP: TBL has affection for HR
<Steven> unexplained affection
<Tina> Do we need HR when we have SECTION?
"There isn't mentioned a single use case. Only some presentational issues
that should be kept in CSS as mentioned in 1.1.1. Right?"
<Steven> no TIna, we don't
SM: don't understand point of comment
GJR: hell, lets deprecate all BLOCK* elements in favor of CSS
SM: lets disucss separator
... TBL has affection for HR - does that mean need HR deprecated in favor of SEPARATOR?
SP: from fundamental point of
view, solves problems with HR - found use cases for separator,
could do with SECTION, but SEPARATOR is useful markup
... problem with HR - presentational; rather than introduce VR, use SEPARATOR
RM: should say HR has no semantic meaning but is shorthand for SEPARATOR
proposal: rename SEPARATOR to HR and add note: "there is nothing horizontal or presentational implied by HR"
SP: first element not related to concept
RM: should be there for legacy, but if starting afresh use SEPARATOR
SP: reason for caring is that saying that won't change ingrained understanding of HR no matter what we say
RM: how do languages that want VR handle HR?
SP: maybe HR only works
horizontally and are using borders on DIV for visually
approximations of vertical rules
... i18n complaint still valid
RM: only if say HR has semantic meaning other than as shorthand for SEPARATOR
SP: have to provide standard stylesheet for XHTML2 - have to provide default style for SECTION, H, etc.
SM: don't think SEPARATOR an
HR
... HR is a styled line running horizontally across page
... separator is semantic indication that one part of document different from another - can be reflected in style rules or not
HTML5: "The hr element represents a paragraph-level thematic break, e.g. a scene change in a story, or a transition to another topic within a section of a reference book."
RM: suggest we move on for now
"Contexts in which this element may be used: Where flow content is expected."
SM: next comment: ABBR should use
something other than @title - we do, so that is moot
... next comment: CITE element
>
GJR: Finally, a for/id relationship between the Q element and the CITE element, which allows the author to bind individual quotes to a common source.
<Steven> I think this is another element rendered unnecessary by rdfa
GJR: should be able to point to
CITE element with for/id relationship
... if @cite is retained should be for human processing
SM: disagree
... src is used to identify external source that is only read-in; href is used for hyperlink; cite is something else
... in current XHTML2 @cite is an @href that is actionable through an alternate method
GJR: a quote is embedded content
<Steven> I think it is actually equivalent to rel="cite" href="...."
<ShaneM> <quote src="someURI" />
<alessio> yep
SM: @src brings in a URI and replaces Q
GJR: . "
SM: @cite is legacy - existed in
HTML4; has different semantic than @href
... drop @src
... @href and @cite similar
... not sure how dovetails with RDFa
... arguable that @cite is something RDFa should process but didn't define rules for that
GJR: @href for Q points to content in context; @src for Q points to source of quote
SP: rel="cite"
SM: will bring up in RDFa telecon
cite in HTML4x
RM: are we done with AVK's comment on cite?
SM: fixed examples
... KBD element
current XHTML2 wording: "The kbd element indicates input to be entered by the user."
SM: response: not in our scope
RM: agree
SP: agree
GJR: agree
<alessio> agree
SM: AVK's next comment - use case for L is bad and doesn't BLOCKCODE preserve whitespace
<Steven> sorry, dropped the phone, just a moment
GJR: BLOCKCODE versus PRE
... PRE literally as-is
... BLOCKCODE can signal to assistive tech to respect and count whitespace
SM: BLOCKCODE doesn't preserve whitespace - layout attribute is irrelevant
GJR: point simply that whitespace
is extremely hard to communicate to a non-visual user
... python examples should be in BLOCKCODE rather than PRE
SM: made note to change
example
... don't want to loose this thread
GJR: will try and explain more clearly
<scribe> ACTION: Gregory - send post to list explaining concerns over PRE [recorded in]
<trackbot> Created ACTION-70 - - send post to list explaining concerns over PRE [on Gregory Rosmaita - due 2009-04-02].
RM: HTML5 backtracked on Q to HTML2
SM: comment "why should be done in text and not stylesheet";"
... favors a SINGLE quote element
... BLOCKQUOTE has?
SM: next comment - why an A
element - answer: backwards compatibility
... why can't one use more than one CAPTION in a list?
SP: CAPTION for entire list, not part of it
26634
GJR: so are we in effect setting up a cascade that says CAPTION for whole item, LEGEND for components?
SM: don't have LEGEND element anymore
GJR: i've been working within PF to reuse the LEGEND element in HTML5
<ShaneM> (confirmed - we no longer have a legend element in XHTML 2)
GJR: since XForms carries LABEL, and LEGEND is no longer needed for the FIELDSET model that LEGEND be reused as an organizational grouping desceriptor
RM: labelling a different discussion
some thoughts on LEGEND:
SM: 10 more items in AVK's list
RM: next address 13.1
<Steven> thanks Gregory!~
my pleasure
==== ADJOURNED ====
This is scribe.perl Revision: 1.135 of Date: 2009/03/02 03:52:20 Check for newer version at Guessing input format: RRSAgent_Text_Format (score 1.00) Succeeded: s/would be/Ben stated that it would be/ Succeeded: s/not feasible/not my idea of fun at the moment :-)/ Succeeded: s/a) , b), c), / a) ; b) ; c);/ Succeeded: s/feedback/input/ Succeeded: s/traker/tracker/ Succeeded: s/what UA wants/what UA can handle/ Succeeded: s/onlly/only/ Succeeded: s/une/unne/ Succeeded: s/SM: rel="cite"/SP: rel="cite"/ Succeeded: s/BLOCKQUODE/BLOCKCODE/ Found Scribe: Gregory_Rosmaita Found ScribeNick: oedipus Default Present: Roland, Gregory_Rosmaita, +46.7.06.02.aaaa, Markus, Steven, Alessio, ShaneM, Tina Present: Alessio Gregory_Rosmaita Markus Roland ShaneM Steven Tina Agenda: Got date from IRC log name: 26 Mar 2009 Guessing minutes URL: People with action items: - gregory post send shane steven talk WARNING: Input appears to use implicit continuation lines. You may need the "-implicitContinuations" option.[End of scribe.perl diagnostic output] | http://www.w3.org/2009/03/26-xhtml-minutes.html | CC-MAIN-2013-48 | refinedweb | 7,197 | 55.27 |
I believe that Mandrill etc give a better deliverability compared to SES.
I believe that Mandrill etc give a better deliverability compared to SES.
Sendy uses SES to send the emails on our behalf - so far so good - we do a weekend update to about 1500 address (so far) and it's worked quite well.
Someday I'll script something to dumb the current user email list into sendy so I don't have to export it to csv and reimport it every weekend...
On reflection, the books I got the most out of that actually shaped my behaviour are...
THE PERSONAL MBA, JOSH KAUFMAN
Was blown away by this. Couldn't believe how much stuff I didn't know about. It covers everything you've asked about and more...
It's also written a bit like a Software Patterns/Recipes book, which I love.
I've read the MBA book about 5 times....
PITCH ANYTHING, OREN KLAFF
You'll hate reading it. It will make you cringe. It's uncomfortable.
But it changed my attitude to business, my products, and deals a LOT. Which is REALLY important.
Applying some of these techniques had amazing results in any dealings with 3rd parties (sales, partnerships, deals). That's because I'm a softie engineer, not a battle-hardened business man. I still read this before attending any significant meeting....
HOW TO BE THE LUCKIEST PERSON ALIVE, JAMES ALTUCHER
Covers everything in one way or another...
I keep coming back to the epic rule list in this book. I keep ignoring them in business, then learning the hard way that the list is right. He shares his failures and successes in a humerous way.
It's a real down-to-earth, eye opening book.
OTHER
I'm reading Lean Startup, and have read Made to Stick, Letting go of the words, Ignore Everybody, Spin Selling, and tons more. All good books, but the 3 above were the biggest impact for me on all levels.
Using bootstrap or another UI Framework would surely improve many things, from the UX/UI side. At least it will help until a pro UX can work on it a lot more.
Bootstrapping also will make you code better since the foundation of the code is well done. It also works on mobile and it's easy to catch up as well to tell other developers to manage our codebase, bootstrap has good documentation online and you can do, practically, almost all kind of UI compositions with JS.
After that, I would follow Google Pagespeed recomendations to reach the 100 points and have something like my blog wich loads in 300ms-500ms.
- You're not utilizing the whole width of the page, and the table looks pretty compressed, making it difficult to read.
- You're also not using the whole height of the page. The pagination would be more useful if there was more content. It's silly to waste that much real estate.
- The icons in the top right are too small and the third (mailing list) carries no meaning.
- Your logo in the navbar is too small, or at least the text. You probably don't need the text in the logo if you've got the heading there.
- Search is in a pretty unintuitive location - try putting it in the top right of the layout.
Edit: From a functional perspective, you've got duplicated stories on the home page currently. Same exact link, two different titles.
I haven't tried Digg or AOL Reader since they aren't available. My usage is basically a headline view of all the feeds, I have them in different catalogs. I will scroll through them to see anything worth to read, and open it up as a new tab as i go through them all.
Newsblur is very non Google Reader like. I suppose it fits some of the pattern of flows of a particular niche. But not me.
Yoleo is great except it doesn't work very well with non Unicode Feeds and it is quite slow. Unread count is overlapping. I think it is a solid app given some more time to develop. But I use Reader everyday or every 4 - 6 hours i cant afford to wait.
Feedly web works well so far. It is the closest thing to Google Reader in Headline views. The thing i dont like are performance and slow scrolling in some cases. But it generally fits me well.
The thing is, there is nothing wrong to try everything out. It is only a click of a button for your Google Login.
After trying a few other services and apps, I switched to NetNewsWire, which is a client-side Mac app that does what I want. Pretty happy so far.
Aside from this, however, I would have gone with Old Reader. Feedly is a good choice (especially with their new cloud platform), but last time I checked, they didn't let you export your feeds. If you don't mind that, Feedly is a great choice.
Minimal, self-hosted, great codebase, implements a clone of Fever's API so it can be used with any mobile client that supports Fever.
Then zap it with my DSLR. Or if it needs to be published, use Dia and export SVG/png into target document.
I occasionally write out graphviz stuff from my code using a very light weight library I wrote (C struct to stdout) if I'm trying to visualise what is in memory at a point in time. This has been invaluable whilst knocking up a simple mark-sweep GC for a project I was working on.
When you get to show the results to others - just use whatever you are presenting the rest of the message with - almost all "office" type products have sufficient capacity to manage that part. The clever bit is the bit you do by yourself. has been my favorite service as it is free for simpler projects and can be upgraded if you need more complexity. I've watched the project grow from an idea, to recruiting developers in my CS classes, to a full blown project which has exceeded my expectations. It's exciting to watch!
It's good for quick diagrams when you need to explain some of the more bizarre architectural choices in your system.
Steep learning curve, but there are plenty of examples around the Internet, and it's certainly worth the investment.
- Dia
- Microsoft Visio (when available, makes nicer diagrams than above, but sucks at anything software modeling related)
- Enterprise Architect is supposedly the standard for the enterprise corp I work for.
I'll add any new ones that are included in the comments here.
Sequence diagram:
Also for the corporate world where only Microsoft tools are an option, I tend to just use MS Word, you can make diagrams that are good enough to get the message across, yet everybody has access to it without requiring a special license.
It makes good looking diagrams very quickly without hampering creativity. It requires almost no effort on formatting and beautification.
I wish they had an app for the desktop. People have requested the same on their forums a few times.
dia ()
[1]:
I'm working on a tool to parse Objective-C into yUML at the moment-
as far as serializing, ujson is 7x faster than simplejson in the worst cases I've seen (disclaimer: using the Python bindings.)
[1]
[2] - "A more user friendly layer for decoding JSON in C/C++ based on [..] UltraJSON"
n.b.: There also exists a class of "simplified" JSON serializers. They implement most of the JSON specification but leave out some features (or restrictions) that make it more expensive. I don't know anything about these, perhaps another commenter can chime in.
(Originally By John Keats)(Originally By John Keats)
No, no, go not to Tor, neither private mode, Nor duck-duck-go the tight-rooted, for its secretive wine; Nor suffer thy pale forehead to be kiss'd By anti-cloud sentiment, ruby grape prose of NSA; Make not your rosary in tinfoil hats, Nor let the politicians, the doomsayers-media be Your mournful Psyche. The downy social media HN, Or on the rainbow of the salt sand-reddit, Or on the wealth of globed nerds from afar; Or if thy mistress some rich anger shows, Imprison her harsh hand, and let her rave, And feed deep, deep upon her peerless eyes. She dwells with GovernmentGovernment that must die; And NSA, whose hand is ever at his lips Bidding adieu; and aching Pleasure nigh, Turning to poison while the lying-mouth sips: Ay, in the very temple of Delight Veiled Melancholy has her sovereign shrine, Though seen of none save him whose strenuous tongue Can burst Joy's grape against his palate fine; His soul shalt taste the sadness of her might, And be among her cloudy trophies hung.
specific prohibitions for fourth amendment abuses
better whistle blower protecting legislation
supporting constitutional amendments for all of the following; ending corporate personhood, enacting real campaign finance reform, restoring Glass Steagall)
breaking up all too big to fail corporations
when enough money or risk to life is involved making it a capital offense/ treason to: supply false testimony to congress or government regulators, etc, or to disseminate false information to the public or business (eg LIBOR distortions), or to unnecessarily make classified any such information
smaller, better government through 'government as a service' Govt 2.0 ideas (see g.g. Lessig), testing legislators on content of bills before they can vote on them, line item vetoes
This party would recruit its candidates (not accept those who nominate themselves) through a computerized equivalent of the way honeybees choose a new nest (see Sealey Honeybee Democracy). Candidates would have to have a track record of volunteer service and a minimum history of published political writing addressing actual legislation - (likely drawing heavily on bloggers and academics).
A question about a relevant product is welcome in Ask.
The officer selection program screens individuals for potential to lead and thrive in a variety of very stressful situations THEN once they've screened for top performers they assign them a job and train them how to do it.
A completely different process than most companies who expect all of their talent to show up with a very specific skill set. Unfortunately this leads to some amazing people being excluded for the talent pool because "it is too much work to train" someone. If one learns the traits to look for I'd guess that training them becomes a breeze and you'll end up with a better hire who will stick around in the long run.
1. Write a list of things that you need to do each really small implementations and keep it in front of you (I use google calendar tasks and keep it in an open tab next to you). Each time you finish a task highlight it or check it off. After a while, each unfinished bullet point will start to bug you especially the longer its been unfinished (at least for me). This helped me finish tasks I hate just because I hate it being the only unfinished task on my list.
2. I can't remember where, but I once read a statement by a coder who said that if a change is too hard implement [in code] restructure the code so that the change is easier to do. I would suggest that whenever you need to work with a section of code that you rewrite it so that you understand it better and can work with it. After all, its your project now, not the old developers. This will take time, but if you plan to stay with the codebase for a while, it might be the better option.
3. And then of course, you could just chug away at the project and work your way through it. If you just want to finish it hard and fast, I would suggest the Pomodoro Technique. I always prefer #1 than the pomodoro, but I've read a lot of people that swear by it, so it probably has some value.
I'm sure this will attract some jeers, but I'm not saying this is explicable and robust science--but it got me the desired effect.
There is this open source game server; the architecture overview page shows you the typical MMO architecture...
There's also a demo called LordOfPomelo; a fully functioning MMO written in Node.js:...
Work with the ones who do want to work with you, do good work and let upper management know about it, and wait for the other ones to get on board.
Here's one example to get you started:...
[1]
We built an algorithmic trading system, and almost everything else in Haskell. Our code base is over 100K of human written code.
The major library gaps were a time library (you can find a version of what we have been thinking about releasing at). We use our own build system that drives cabal and ghc. Otherwise having many libraries is just painful.
We found that composing applications as conduits to be a very effective design pattern that minimizes many laziness issues. Monad transformers are very powerful but the machinery for them (like forking) is not fully cooked.
Maintaining the codebase is far easier with haskell than with anything else I have worked with (C/C++,C#,Java,etc...). Refactoring in Haskell is great.
You can't fight the language. Fighting with Haskell will cause great pain. When you go with the flow, using lots of strong types, higher order functions and can apply things like a monoid instance to a problem the language is a joy to work with.
Debugging is more painful than it has to be. There are still times when you need some real GDB wizardry.
Lastly if you have more questions feel free to contact me through our website
STM can exhibit something that looks a hell of a lot like livelock.
Error handling is brutal. Catching all classes of exceptions (at the place you want to catch them!) for recovery is surprisingly tricky. This isn't necessary in theory with things like MaybeT, but in practice, lots of odd libraries use things like partial functions and the error function.
Not having tracebacks in production code is painful
The library community is thriving but it has a lot of volatility. Things break each other quite frequently. Semantic versioning either isn't enough to save it or hasn't been adhered to strictly enough.
Thunk leaks and other consequences of unexpected laziness aren't as common as people worry about, but they're kind of a pain to track down when they occur
Strict vs. Lazy bytestrings, String, Text, utf8-string, etc. You may find yourself doing a lot of string/bytestring type conversion
There's still wars raging about the right way to do efficient, safe I/O streams. Conduit vs. Enumerator vs. Pipes etc. They're all turning into pretty compelling projects, but the fact that there are N instead of 1 is sometimes a drag when you're dealing with libraries and dependencies.
There are not a lot of good open source "application server" type frameworks that really handle thread pooling, resource exhaustion, locking, logging, etc, in robust nice ways. We have one internally, and I'm sure a bunch of other haskell-using shops do too, but the ones on hackage are not nearly sophisticated enough (IMO) and I suspect not very battle tested against the kinds of ugly queuing problems you run into in highly loaded environments.
If I think of more, I'll add em... these are off the top of my head.
1. Modifying a record value (that is, making a copy of a record value but with different values in one or two of its fields) is unnecessarily complicated and uncomposable. This makes modifying a subfield painful.
2. Field names are in the global namespace. Thus you cannot have e.g. a field named `map` (conflicts with the standard `map` function); nor a local variable named `owner` in the same scope that you use a field named `owner`; nor may two different record types both have a `name` field. C had this problem in the 70s (which is why e.g. struct tm has tm_sec and tm_min fields instead of sec and min fields), but they solved it a long time ago.
The solution to deficiency 1 is to use lenses. Use the lens package from Hackage, but don't read its documentation at first: it generalises the problem exceedingly well, but this makes it harder to understand at first glance. Instead seek out a basic tutorial. At the cost of a short line of boilerplate for each record type, this works well.
There is no satisfactory solution to deficiency 2. Some people define each record type in its own module, and import each module qualified. I don't think this scales well. I prefer to put a record-type prefix on each of my field names (i.e. the same thing C programmers were forced to do in the 70s).
Instances can't be explicitly imported either.
Another thing I don't like is if you have two different functions with the same signature but different implementations meant to give swappable functionality, there's no way of specifying that explicitly. As a user of a library, you just have to realize the functions can be swapped out with modules. For example:........
It's really not that bad but I do like how other languages allow the programmer to make this explicit.
The one issue I've run into is that ghc can't cross compile. If you want to run your code on ARM, you have to compile an ARM version of ghc (QEMU comes in handy here).
edit: to clarify on the web thing, when I say "on your own" I mean you won't be able to get much from existing tutorials and examples since you will want to do everything differently. Not that you will have to write your own framework.
1. Way to many user defined operators. Haskell lets you define almost anything as an infix operator which library authors love to (ab)use. So you get operators like ".&&&." (without the quotes) because they are functions reminiscent of the boolean and operation.
2. But weirdly enough, many operators aren't generic. String concatenation is performed with "++" but addition with "+".
3. Incomplete and inconsistent prelude. It has unwords and words for splitting and joining a string on whitespace. But you dont get to specify what string to use as the delimiter like the join and split functions in other languages lets you do.
4. So instead you have X number of implementations of splitStringWith on Hackage, some of which are unmaintained, deprecated or just not working, meaning that just answering the question "how should I split a string?" becomes a big endeavour (...).
5. There are four different "stringish" types in Haskell: List, LazyList, ByteString, LazyByteString. A function like splitStringWith works on one of the types, but not the three others for which you need other functions. Some libraries expect Lists, other ByteStrings or LazyByteStrings so you have to keep converting your string to the different types.
6. Most Haskellers seem to content with just having type declarations as the api documentation. That's not a fault of Haskell per se, but imho a weakness in the Haskell community. For example, here is the documentation for the Data.Foldable module:
7. This is very subjective and anecdotal but I've found the Haskell people to be less helpful to newbies than other programming groups.
Working with DBs is easy, especially if you use HaskellDB. There are bindings for non-relational DBs, as well as a DB written in Haskell (acid-state).
As for the language itself, you might find it tricky to develop computation intensive applications with large run-time data-sets due to garbage collection (but that is true for any garbage collected language). Other than that, it's one of the best performing languages in the Debian PL shootout. And the fact that concurrency is (comparatively) easy means you can make use of those extra cores.
Monad transformers and monads are fine, you just need to learn how to use them.
To sum up: it depends on what you do and what you consider a "real world application". Might be a good idea to elaborate. For example, are compilers, games, web apps, automated trading systems, android apps considered "real world"? Because any of these has been done in Haskell.
Achieving performance is harder than in c or c++.
The ecosystem is strong on some counts and weak in others.
There's lots of API duplication (lazy/strict byte strings, map, set, seq, etc).
Good performance may depend on brittle ghc optimizations that might break in very difficult to comprehend ways if ghc is upgraded.
After using Haskell pretty much full-time for 10 years, writing C and Java code makes me sad. The support for the above mentioned platforms is in-progress, but is not yet mature.
There are some neat things like Atom which use a Haskell DSL to target arduino.
My other issue is that the garbage collector in GHC is not really sufficient for real-time audio applications because it can pause for too long. GHC HQ has tried to tackle this in the past -- but there is a reason why it is a research topic :)
If your application requires interfacing to a C++ world -- your are not going to have fun. Though there might be a GSoC project for that this summer?
Also, GUI stuff is somewhat lackluster. There are bindings to gtk, etc. And they can get the job done. But they don't really capture the essence of what makes Haskell awesome. We are still searching for the GUI abstraction that really clicks.
It makes me wondering what magic would happen when those folks can work on helping the ecosystem full time!
I have to say that one of my favorite things currently about haskell is how nice and easy the c ffi is to use. So darn simple! (I'm also GSOC mentoring some work to provide a nice C++ ffi tool too).
Theres so many great tools in the Haskell ecosystem, for every problem domain. Its not perfect, and theres always room for more improvement, but those improvements are happening, and the more people invest in supporting the community, the more those improvements happen!
For example, one thing i'll be exploring in the neat future is how to do good Numa locality aware scheduling of parallel computation. It looks like i might be able to safely hack support in via a user land scheduler (though i'll find out once i get there).
My principal work right now is building numerical computing / data analysis tools, and some of the things I'm doing now would be simply intractable in another language....
My project is targeted at the Market Research industry.
a. There is a survey programming compiler, written in yacc (bison)/C++.
b. I also have a cross tabulation engine (another compiler part of the same project), which presents a web interface for Cross tabulation engine (I am using webtoolkit.eu).
The survey compiler can currently compile to UI front ends like:ncurses, webtoolkit, wxWidgets and gtk. The GUI frameworks are all in a very nascent stage. I have also been experimenting with emscripten and using frameworks like dojo and dojomobile. I have been able to get dojo working.
There is also a Random Data Generator, built on the Survey engine.
There is work to be done in the Cross tab engine as well. There is a branch where I am experimenting with SSE instructions to speed up the engine.
Scope of work is wide and I can get help you get started with anything you find interesting to work on. The project is open source and hosted here:
website:
Active git branches: nc, web-questionnaire-2, rdg, xtcc
You can email me at "nxd" underscore "in" at yahoo dot com
Unfortunately we are a single person startup and no funding, everything is being done my me at the moment. If you are looking for something like this to start an interning/job relationship, then this might not be the best project.
Thank you for your offer once again and hope you get something that is a close fit to what you are looking for.
I'll give you a project...all specced out...details on trello...you can take from open source projects already slightly ahead of us...graphics as needed...
And if you can build a working proto that the client approves (which I've already sold), I'll even pay you.
Interested? What's your story?
Steve Brettsteven.b.brett@gmail.com
Discussion of SSL on cryptome:
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I've restarted once because something in Safari locked the whole phone. Some apps are broken (Podcasts), or look wonky in spots (Find My Friends). Everything mostly works, though. Even the Pebble app to connect to the Pebble watch. I figured if anything would break, it would be that.
If you want everything to work all of the time, never put the first iOS beta on your phone. Something is always not right. (Last year I was at WWDC, and the new maps app wouldn't render maps for me, just a grid. Not knowing SF that well, that was a major breaking change for me. <G>) Wait until beta 3 or so if you need reliability.
I can deal with all the other issues, but terrible battery life is a dealbreaker. I'll hold off putting it on my primary phone until it improves.
As for bugs and such, I haven't encountered any that would stop me from using the beta or are frustrating. The only app I have right now that crashes on my is Google+.
Have had a few issues with apps, most notably the Apple podcast app which is completely broken. Had one incident where the lock screen was totally blank other than the top bar but was fixed by a restart.
Pros ~ Two words - Control Center. I can easily change anything that I want without jailbreaking. It seems like they are moving towards an SBSettings-like iOS. For reference, SBSettings is a jailbreak-only package that allows you to change nearly every aspect of your iDevice.
Cons ~ Some apps are broken and will just not really work (ie. Alien Blue) with iOS 7 yet. Lag is very small but just enough to be noticeable. Restoring from a backup may take overnight, depending on the amount of data you already have. Some features can take some getting used to before you feel comfortable (ie. displaced 'delete' button when typing in passcode).
Don't forget that certain apps will not work. For example, neither the eBay app or MLB apps are working for me (and I use those everyday too).
Facebook is private surveillance
I wont classify, I wont categorise and I won't tag, I will not create albums, I will just keep uploading everything everywhere. I will try face-detection with different people and my cat. You get the idea.
If enough people over use / abuse the fb with loads of insignificant info, FB's game will backfire.
Its the facial recognition that really creeps me out though, and the fact that cops always are recording cameras at community events and protests. Supplier meet consumer. | http://hackerbra.in/ask/1372190701 | CC-MAIN-2018-43 | refinedweb | 4,629 | 71.85 |
The fact that most metals expand when heated and contract when cooled has serious implications when the dimensions of a piece of laboratory equipment are critical to an experiment. A typical aluminum bar that is w cm wide at 70ºF will be
x = w + (t-70) x 10^-4 cm wide at a nearby temperature t.
Write a program that prompts the user for the standard width of the bar at 70ºF and for a tolerance for width variation. Then write to a file a table like the one below indicating the bar’s width at temperatures from 60ºF to 85ºF in one degree intervals and marking with a star the temperatures at which the bar’s width is within tolerance.
Ideal Bar Width (at 70 degrees F): 10.00000 cm
Tolerance for Width Variation: 0.00050
Temperature Width Within Tolerance
(degrees F) (cm)
60 9.99900
61 9.99910
62 9.99920
63 9.99930
64 9.99940
65 9.99950
66 9.99960
67 9.99970
68 9.99980 *
69 9.99990 *
70 10.0000 *
…
85 10.00150
//My Code so far:
#include <vcl.h>
#include <conio>
#include <iostream>
#include <fstream>
#include <cmath>
#include <iomanip>
using namespace std;
double x; //result of the equation
double t; //temperature
const double AL = 70; //standard temp for standard bar
double w; //width of the bar
char tolerance; //within tolerence
int main ()
{
cout<<"This program will let you know if a bar is in tolerance or not."<<endl;
cout<<"Ideal Bar Width at (70 degrees F): 10.00000 cm) "<<endl;
cout<<"Tolerance for Width Variation: 0.00050 "<<endl;
cout<<"Enter the standard width of the bar in centimeters (cm) then enter the "<<endl;
cout<<"temperature in Fahrenheit. (use a space between the inputs)" <<endl;
cin>> w >> t;
x = w + (t - AL) * .0001;
if (x < 9.99950 || x > 10.0005) //outside this range is out of tolerance
tolerance = 95;
else if (x <=10.00050 && x >= 9.9950) //between these values is in tolerance
tolerance = 42;
cout << setprecision(5); // precision for 5 places after decimel
cout << x <<endl; //trap for x
cout<<"Temperature Width Within Tolerance"<<endl;
cout << t << setw(23)<< w << setw(7)<< tolerance << endl;
getch();
return 0;
}
I am having dificulties figuring out how to
input the range of temperatures and the range of widths into the
code so I can output the table properly. So far I can do each one
individually.
Any help would be appreciated. | http://www.chegg.com/homework-help/questions-and-answers/fact-metals-expand-heated-contract-cooled-serious-implications-dimensions-piece-laboratory-q3033282 | CC-MAIN-2014-52 | refinedweb | 406 | 67.86 |
| Hopefully this is it (barring a rename on the high level interface. | I missed the CPPFLAGS in the last version.. | If you're code is portable this is effective with a simple | AC_API_WIN32 You should really read the CVS Autoconf documentation. Your quotation is dangerous at some points, and there are a few suggestions in there on how to unobfuscate M4 code. | dnl COMPILER WIN32 support ==================================== | AC_DEFUN(AC_PROG_CC_WIN32, [ | dnl figure out how to run CC with access to the win32 api if present | dnl configure that as the CC program, | dnl WIN32 may be present with WINE, under cygwin, or under mingw, | dnl or cross compilers targeting those same three targets. | dnl as it happens, I can only test cygwin, so extra input here will be appreciated | dnl send bug reports to Robert Collins <address@hidden> | | dnl logic: is CC already configured? if not, call AC_PROG_CC. | dnl if so - try it. If that doesn't work ,try -mwin32. If that doesn't work, fail | dnl | dnl 2001-03-15 - Changed from yes/no to true/false -suggested by Lars J Aas<address@hidden> | dnl * Change true to : - suggest by Alexandre Oliva <address@hidden> | dnl * changed layout on the basis of autoconf mailing list: | dnl there are now two interfaces, a language specific one which sets | dnl or clears WIN32 && WIN32FLAGS as appropriate | dnl Move the comments out of the macro, use `#', not dnl, quote the name being defined. | AC_REQUIRE([AC_PROG_CC]) dnl at the end | echo $ECHO_N "checking how to access the Win32 API..." >&6 This is wrong, use the AC_FD_* if you need to, otherwise you certainly mean AC_MSG_* | WIN32FLAGS= | AC_TRY_COMPILE(,[#ifndef WIN32 | #ifndef _WIN32 | #error WIN32 or _WIN32 not defined | #endif | #endif], #error is suspected to cause problems, although I don't recall having seen it happen. Please indent cpp directives. | [ | dnl found windows.h with the current config. | echo "${ECHO_T}Win32 API found by default" >&6 | ], [ You must not use ECHO_N, you are breaking the abstraction layers :) | dnl try -mwin32 |&6 |&6 | ]) | ]) | | AC_PROVIDE([$0]) Huh? Don't, AC_DEFUN did for you. | AC_DEFUN(AC_PROG_CXX_WIN32, [ Same comments. | AC_DEFUN(AC_API_WIN32, [ | dnl high level interface for finding out compiler support for win32. | | AC_LANG_CASE([C], AC_PROG_CC_WIN32 [CFLAGS="$WIN32FLAGS $CFLAGS" | CPPFLAGS="$WIN32FLAGS $CPPFLAGS"], | [C++], AC_PROG_CXX_WIN32 [CXXFLAGS="$WIN32FLAGS $CXXFLAGS" | CPPFLAGS="$WIN32FLAGS $CPPFLAGS"], | [echo "No macro support for WIN32 with $_AC_LANG" | exit 1]) | ]) Use AC_FATAL. Quote the exec parts. And in fact, just factor AC_PROG_CXX_WIN32 as an AC_REQUIRE of this macros. | http://lists.gnu.org/archive/html/autoconf/2001-03/msg00129.html | CC-MAIN-2014-52 | refinedweb | 405 | 70.94 |
I'm trying to make a script that resize multiple or a single image based on a data pulled from XML. My question is if i have multiple images how can I print out a qusetion like "There are more than 1 image do you wish to resize image 2 also?... than maybe " Would you liek to resize image 3 also ?"
My script so far is as follow,the only problem is taht it resizez all the images at start :
import os, glob import sys import xml.etree.cElementTree as ET import re from PIL import Image pathNow ='C:\\' items = [] textPath = [] imgPath = [] attribValue = [] #append system argument to list for later use for item in sys.argv: items.append(item) #change path directory newPath = pathNow + items[1] os.chdir(newPath) #end #get first agrument for doc ref for item in items: docxml = items[2] #search for file for file in glob.glob(docxml + ".xml"): tree = ET.parse(file) rootFile = tree.getroot() for rootChild in rootFile.iter('TextElement'): if "svg" or "pdf" in rootChild.text: try: textPath = re.search('svg="(.+?)"', str(rootChild.text)).group(1) attribValue.append(rootChild.get('elementId')) imgPath.append(textPath) except: continue for image in imgPath: new_img_path = image[:-4] + '.png' new_image = Image.open(new_img_path) new_size=int(sys.argv[3]), int(sys.argv[4]) try: new_image.thumbnail(new_size, Image.ANTIALIAS) new_image.save(new_img_path, 'png') except IOError: print("Cannot resize picture '%s'" % new_img_path) finally: new_image.close() print("Done resizeing image: %s " % new_img_path)
Thank you in advance.
Zapo
Change your final loop to:
for idx, image in enumerate(imgPath): #img resizing goes here count_remaining = len(imgPath) - (idx+1) if count_remaining > 0: print("There are {} images left to resize.".format(count_remaining)) response = input("Resize image #{}? (Y/N)".format(idx+2)) #use `raw_input` in place of `input` for Python 2.7 and below if response.lower() != "y": break | https://databasefaq.com/index.php/answer/3399/python-xml-image-resize-python-resize-multiple-images-ask-user-to-continue | CC-MAIN-2020-10 | refinedweb | 304 | 51.34 |
Created attachment 1678 [details]
Common.Localization
I have a common project with the localization info for all my apps, Common.Localization.csproj. In order for the localization, like fr.lproj to appear in the resulting build, I have to create a dummie class in the common project, wrap it with a [Preserve] attribute AND reference it in the app.
If there is no dummie class made, there is no common.localization.dll made and the localization files are not sent to the .app
Here's how I make it work:
Create a dummie class in common.localization.csproj
using System;
using MonoTouch.Foundation;
//Needed to make this DLL compile and have it's resources included
namespace Common.Localization
{
[Preserve]
public class DummieClass
{
[Preserve]
public DummieClass ()
{
}
}
}
Now in the AppDelegate
var d = new DummieClass();
d=null;
Then it works.
I am hoping this is a bug as I'd rather not have write dummie references in all my apps just to get the localization copied over to the app. It's be ok if I just have a dummie class with [Preserve], but to have to reference it too?
Photo attached.
Version info:
MonoDevelop 2.8.8.4
Runtime:
Mono 2.10.9 (tarball Tue Mar 20 15:31:37 EDT 2012)
GTK 2.24.10
GTK# (2.12.0.0)
Apple Developer Tools:
Xcode 4.3.1 (1176)
Build 4E1019
Monotouch: 5.2.10
That's likely a linker issue, i.e. removing an assembly without any code left inside it. I'll check this, thanks for the bug report.
So this is not a linker issue (the same thing occurs, on device, without linking). Once compiled there's no reference to the assembly and it is (presently) ignored (i.e. not copied) even if it contains resources.
Your workaround ensure a reference is compiled in (so it's not excluded for being extraneous) and the [Preserve] ensure the code is not linked out (which could remove the reference when linked).
> It's be ok if I just have a dummie class with [Preserve],
We might be able to remove this requirement. E.g. if there's no code but some resources are present then we could copy the assembly in the bundle.
That needs some testing so we do not end up with SDK assemblies (that include resources) requiring extra space in applications (for unused resources).
> but to have to reference it too?
Sadly that requirement is harder to remove.
Without a reference mtouch would not even know about the resource assembly (as it would not be on its command line) and the tool cannot just bring every .dll it finds (some solutions have a lot of extraneous assemblies that are not meant to be shipped with the app).
Now we could have another way to "mark" them but it would not be any simpler than the (existing) "add reference". Also there is IMO a reference between them - as the main app will refer to the resource-only assembly.
In this case I would say the risk-reward is not favorable. I recommend leaving it as is.
This bug was targeted for a past milestone, moving to the next non-hotfix active milestone.
It's now possible to preserve a type from another assembly, e.g.
> [assembly: Preserve (typeof (Common.Localization.DummieClass))]
which reduce a bit the code required in both the main and resource .dll. However it still requires a reference to exists. | https://bugzilla.xamarin.com/show_bug.cgi?id=4453 | CC-MAIN-2016-07 | refinedweb | 575 | 66.84 |
I'm running "Exodriver example", which counts Labjack devices that are physically connected. I modified it to open a U12 if found. It works (LJUSB_OpenDevice returns a large int) right after I plug the U12 in, but after I restart the Mac it can't open the U12 (the returned handle is 0). Below is main.c. My mods start with the if statement. (This problem didn't happen with MacOS 10.10 and earlier)
#include <stdio.h>
#include "labjackusb.h"
int main (int argc, const char * argv[]) {
printf("How many LabJacks are connected?\n");
int numU3s = LJUSB_GetDevCount(U3_PRODUCT_ID);
int numU6s = LJUSB_GetDevCount(U6_PRODUCT_ID);
int numUE9s = LJUSB_GetDevCount(UE9_PRODUCT_ID);
int numU12s = LJUSB_GetDevCount(U12_PRODUCT_ID);
printf("U3s: %d\n", numU3s);
printf("U6s: %d\n", numU6s);
printf("UE9s: %d\n", numUE9s);
printf("U12s: %d\n", numU12s);
if (numU12s > 0) {
HANDLE han;
printf("Opening the first U12\n");
han = LJUSB_OpenDevice(1, 0, U12_PRODUCT_ID);
printf("Handle: %d\n", han);
LJUSB_CloseDevice(han);
}
return 0;
}
A typical result of running it under MacOS 10.13.3, High Sierra, is (when the Open succeeds)
How many LabJacks are connected?
U3s: 0
U6s: 0
UE9s: 0
U12s: 1
Opening the first U12
Handle: 41945088
Program ended with exit code: 0
EDIT: I have both LabJackHID.kext and LabJackNoHID.kext in /System/Library/extensions. Is that normal?
If you power cycle your U12 now after your reboot, can your application find the U12? Or in general after your reboot the U12 can't be found?
Check that the U12 LED is on to indicate it is enumerated. Also, you can check System Information and in USB see if you can see the U12.
Make sure no other application has your U12 open since only one process can claim a USB device. If you have another application, make sure it closes the U12 before another application tries to open it.
Make sure that the LabJackHID.kext is not blocked. The U12 requires this kext file to prevent the Mac HID driver from claiming it, and so libusb can open it. macOS 10.13 introduced "User-Approved Kernel Extension Loading", so you may need to allow the kernel extension. Double check your "Security & Privacy" and make sure it isn't blocked. This page here shows the Security & Privacy window and what to look for.
Thanks for all the info. Sorry I forgot to mention that it starts working again if I unplug/replug cable in computer's USB port.
The Mac can always see the U12 when it is plugged in, and so can the Exodriver example app. The app can see it- it just can't open it until power is cycled.
No other (user-owned) application has claimed the device.
I've visited "Security & Privacy" and there's no indication the kext is blocked. Anyway, this failure occurs in El Capitan and Sierra as well, but not Yosemite. So the problem may have been created by the change from 10.10 to 10.11.
I tried disabling "SIP" using csrutil on a Sierra system and it didn't improve things. I think SIP was introduced in 10.11, the oldest OS with this problem.
When I start the Mac there are 4 flashes followed by 2 more, and then the light stays solid green.
We'll try the U12 on macOS 10.13 at the start of next week. U12 hasn't had much testing beyond 10.10, but no one has reported an issue like this until now.
Some other things to try in the meantime:
1. Remove all the LJUSB_GetDevCount calls and just try to open the first U12.
2. After your LJUSB_OpenDevice, use errno ("man errno" for documentation) to see if there is a useful error code. Exodriver sets errnos based on the libusb error:...
Removing the other GetDevCount's didn't seem to help.
The error after restarting is "Permission denied" (13) when the U12 is found but can't be opened. No other app was running, but that's the same error I get when another application is using the device.
Thanks again
Scott
I tested on Mac running macOS 10.13.3 and I didn't see your issue. Running your code and our Exodriver example multiple times found and opened the U12 without problem.
Disconnect your U12, run the installer from the following page, plug in your U12 and see if that helps:
This installs the ljacklm high-level driver, Exodriver, libusb, and LabJackHID.kext. This differs from the Exodriver only installer which makes the LabJackHID.kext optional, so if you used that installer you may have missed installing it. The kext gets installed to the /System/Library/Extensions/ directory.
If you are using OS X 10.11, make sure it is running version 10.11.4 or later. Earlier versions had a USB layer bug where USB close calls were not working, keeping handles open after the process stopped.
Thanks for the suggestions. I am also running 10.13.3. The installer is the same as I have already installed, but I followed your directions. I was able to open the U12 as expected, but after I restarted the Mac I was unsuccessful. When you say you ran the code multiple times, have you been restarting the computer? My procedure:1. Plug in the U12
2. Confirm the U12 can be opened by running the code
3. Restart the Mac with the U12 still plugged in
4. Run the code again to see if U12 can be opened. In my case the answer, over multiple Macs and OS's (except 10.10) the answer is no.
Thanks
Scott
To confirm your issue and what I see, the U12 can only be used if you reconnect it after a reboot. After it reconnects, it runs as expected and a reconnect is not needed until next reboot.
It looks like if the U12 is connected while rebooting or before logging in in general, the system is using the HID driver and seemingly not using settings from the LabJackHID.kext to use the standard USB IO interface for libusb-1.0 compatibility. After logging in and connecting, it starts using LabJackHID.kext. Apple rewrote their OS X / macOS USB layer in 10.11 so when the issue started would make sense, but I'm unsure what changes are causing this.
If what I am describing is your issue, the current workaround is the U12 needs to be connected after you reboot and log in to your Mac. Alternatively there is a Watchdog feature to have the U12 reset on its own every X seconds if there are no communications, though you do not want to turn this on and off repeatedly for flash life.
Keep in mind the U12 is a legacy device and development from us on it is limited as we are focused on our more modern devices which have Mac support without this issue.
Having to reconnect the USB cable is not acceptable. Is the U3 software-compatible with the U12 with regard to MacOS? And can you guarantee that the U3 doesn't have the same problem (Have you tried the same experiment with the U3)?
Thanks-
Scott
OK, I didn't think we had a U3 but someone here was able to locate an old one, hardware V1.21. I modified my modified Exodriver example to find and open a U3, which it did successfully.
And after a restart of the Mac it was again able to find and open the U3! So it doesn't have the U12's problem.
Thanks for your help.
All other LabJack devices do not have this issue as you found out with the U3. Only the U12 is a HID device and uses a kext, and has the issue of Mac loading it as a HID upon system reboot instead of using the kext settings. | https://labjack.com/forums/apple-mac-os-x/cant-open-u12-after-restarting-mac-macos-yosemite | CC-MAIN-2019-22 | refinedweb | 1,310 | 66.54 |
Behind ASP.NET MVC Mock Objects
Introduction:
I think this sentence now become very familiar to ASP.NET MVC developers that "ASP.NET MVC is designed with testability in mind". But what ASP.NET MVC team did for making applications build with ASP.NET MVC become easily testable? Understanding this is also very important because it gives you some help when designing custom classes. So in this article i will discuss some abstract classes provided by ASP.NET MVC team for the various ASP.NET intrinsic objects, including HttpContext, HttpRequest, and HttpResponse for making these objects as testable. I will also discuss that why it is hard and difficult to test ASP.NET Web Forms.
Description:
Starting from Classic ASP to ASP.NET MVC, ASP.NET Intrinsic objects is extensively used in all form of web application. They provide information about Request, Response, Server, Application and so on. But ASP.NET MVC uses these intrinsic objects in some abstract manner. The reason for this abstraction is to make your application testable. So let see the abstraction.
As we know that ASP.NET MVC uses the same runtime engine as ASP.NET Web Form uses, therefore the first receiver of the request after IIS and aspnet_filter.dll is aspnet_isapi.dll. This will start the application domain. With the application domain up and running, ASP.NET does some initialization and after some initialization it will call Application_Start if it is defined. Then the normal HTTP pipeline event handlers will be executed including both HTTP Modules and global.asax event handlers. One of the HTTP Module is registered by ASP.NET MVC is UrlRoutingModule. The purpose of this module is to match a route defined in global.asax. Every matched route must have IRouteHandler. In default case this is MvcRouteHandler which is responsible for determining the HTTP Handler which returns MvcHandler (which is derived from IHttpHandler). In simple words, Route has MvcRouteHandler which returns MvcHandler which is the IHttpHandler of current request. In between HTTP pipeline events the handler of ASP.NET MVC, MvcHandler.ProcessRequest will be executed and shown as given below,
void IHttpHandler.ProcessRequest(HttpContext context)
{
this.ProcessRequest(context);
}
protected virtual void ProcessRequest(HttpContext context)
{
// HttpContextWrapper inherits from HttpContextBase
HttpContextBase ctxBase = new HttpContextWrapper(context);
this.ProcessRequest(ctxBase);
}
protected internal virtual void ProcessRequest(HttpContextBase ctxBase)
{
. . .
}
HttpContextBase is the base class. HttpContextWrapper inherits from HttpContextBase, which is the parent class that include information about a single HTTP request. This is what ASP.NET MVC team did, just wrap old instrinsic HttpContext into HttpContextWrapper object and provide opportunity for other framework to provide their own implementation of HttpContextBase. For example
public class MockHttpContext : HttpContextBase
{
. . .
}
As you can see, it is very easy to create your own HttpContext. That's what did the third party mock frameworks like TypeMock, Moq, RhinoMocks, or NMock2 to provide their own implementation of ASP.NET instrinsic objects classes.
The key point to note here is the types of ASP.NET instrinsic objects. In ASP.NET Web Form and ASP.NET MVC. For example in ASP.NET Web Form the type of Request object is HttpRequest (which is sealed) and in ASP.NET MVC the type of Request object is HttpRequestBase. This is one of the reason that makes test in ASP.NET WebForm is difficult. because their is no base class and the HttpRequest class is sealed, therefore it cannot act as a base class to others. On the other side ASP.NET MVC always uses a base class to give a chance to third parties and unit test frameworks to create thier own implementation ASP.NET instrinsic object.
Therefore we can say that in ASP.NET MVC, instrinsic objects are of type base classes (for example HttpContextBase) .Actually these base classes had it's own implementation of same interface as the intrinsic objects it abstracts. It includes only virtual members which simply throws an exception. ASP.NET MVC also provides the corresponding wrapper classes (for example, HttpRequestWrapper) which provides a concrete implementation of the base classes in the form of ASP.NET intrinsic object. Other wrapper classes may be defined by third parties in the form of a mock object for testing purpose.
So we can say that a Request object in ASP.NET MVC may be HttpRequestWrapper or may be MockRequestWrapper(assuming that MockRequestWrapper class is used for testing purpose). Here is list of ASP.NET instrinsic and their implementation in ASP.NET MVC in the form of base and wrapper classes.
Summary:
ASP.NET MVC provides a set of abstract classes for ASP.NET instrinsic objects in the form of base classes, allowing someone to create their own implementation. In addition, ASP.NET MVC also provide set of concrete classes in the form of wrapper classes. This design really makes application easier to test and even application may replace concrete implementation with thier own implementation, which makes ASP.NET MVC very flexable. | https://weblogs.asp.net/imranbaloch/behind-asp-net-mvc-mock-objects | CC-MAIN-2020-34 | refinedweb | 816 | 53.07 |
Any info in this course regarding the ESP-NOW protocol?
——–
Here’s how to use ESP-NOW with the ESP32:
UPDATE: We’ve published some tutorials about ESP-NOW:
- Getting Started with ESP-NOW (ESP32 with Arduino IDE)
- ESP-NOW Two-Way Communication Between ESP32 Boards
- ESP-NOW with ESP8266 – Getting Started
Hi Steven.
I haven’t experimented with the NOW protocol yet.
Were you successful with the tips from DK?
Regards,
Sara
Hi
Its one of the projects I am working on. Best sources
youtube.com/watch?v=lj-vIBPEI2E
youtube.com/watch?v=6NsBN42B80Q
instructables.com/id/ESP-NOW-WiFi-With-3x-More-Range/
#include <esp_now.h>
#include <WiFi.h>
Hope it helps
Hi .. with NOW I need to know how once it makes a connection to keep sending data without having to disconnect each time. The example shows it sending 1,2,3… but it makes a connection each time.
Hi, These are the projects, that I am using … work fine for me ..
Try a version of this…
while(1) // stay on { getdata(data to be sent); if(data to be sent != NULL) { esp_now_send( date to be sent); data to be sent = NULL or ""; } }
Here is the Protocol:
docs.espressif.com/projects/esp-idf/en/latest/api-reference/network/esp_now.html | https://rntlab.com/question/esp32-now-protocol/ | CC-MAIN-2022-21 | refinedweb | 214 | 59.4 |
Capistrano is oriented so it deploys to the same directory on several machines. This means you can't deploy to two different locations on the same machine. The following recipe in Capfile will allow you to duplicate your main rails app in a second directory. You can schedule it to run automatically with every deploy or just do it manually. I included database migrations by default. Remove the shared config line if you don't have it. Edit the directories to match yours.
namespace :yournamespace do desc "Synchronize main_app to second_app" task :sync_apps, :roles => [:app, :db, :web] do puts "synchronizing main_app to second_app" run "rsync -a /var/rails/main_app/ /var/rails/second_app --exclude=/shared --delete" run "for file in `find /var/rails/second_app -type l`; do TARGET=`readlink $file | sed -e \"s/main_app/second_app/\"`; rm $file; ln -s $TARGET $file; done;" run "cp /var/rails/second_app/shared/config/* /var/rails/second_app/current/config"; run "cd /var/rails/second_app/current; /usr/local/bin/rake RAILS_ENV=production db:migrate;" run "touch tmp/restart.txt" end end
Noel Peden replied on Mon, 2012/05/07 - 6:05pm
This is now done better with the Multitage extension.
Simply create two stages and place different :deploy_to settings in each.
Cici Wirachmat replied on Sun, 2011/10/16 - 11:39am DZone we are helped how to devel Website> | http://www.dzone.com/snippets/capistrano-deploy-rails-twice | CC-MAIN-2014-41 | refinedweb | 222 | 54.32 |
Firefox is a relatively new Web browser and currently the most popular browser built on the Mozilla platform. You've probably heard of it because of its phenomenal growth and its profile as an open source software success story. Perhaps it's even your Web browser of choice, as it is mine. IBM made news earlier this year by encouraging its employees to use Firefox and by standardizing Firefox support with its enterprise help desk. IBM has also been improving Firefox support throughout its product line, including Lotus® Domino®. Other enterprises, impressed by the confidence shown by such a prominent IT company, are moving their internal standards toward Firefox.
One of the advantages of Firefox is that it inherits many XML features from Mozilla. Many of these features have historically been offered partially or tentatively in Mozilla (and Firefox), but in the 1.5 release Firefox made a big leap in the number and quality of XML features. Firefox 1.5 is a good Web browser for XML developers and should help drive the adoption of client-side XML features that have been slow to spread on the Web. It's important to keep in mind that many current developments in Web technologies -- including developments in Firefox browser features -- are making the Web browser an increasingly complete platform for specialized applications development, rather than just a simple tool for browsing the Internet. XML generally plays a significant role in these technological developments, which some commentators refer to as Web 2.0.
In this series, you'll learn about the various XML features in Firefox 1.5. This first article gives you an overview of these features. See Resources for more information about how to grab a copy of Firefox for your own use and development.
From the days of the pioneering Web browser NCSA Mosaic, the role of a browser has been to retrieve the various files that make up a Web page and organize them for user display. The most common formats for such files have been HTML and various binary image formats. XML was originally intended to be SGML on the Web, and its advent has brought with it all sorts of new XML-based formats that Web browsers have had to properly parse and display. The most basic task for an XML-aware browser is for it to be able to prioritize which format is the most important, and Firefox is no slouch in this department.
Mozilla (and thus Firefox) has been able to parse plain XML (including namespaces) in nonvalidating mode for years. By default, it simply displays a simplified view of the XML, telling the user:
This XML file does not appear to have any style information associated with it. The document tree is shown below.
You can embed portable
xml:stylesheet processing instructions in the XML to instruct Firefox to load a CSS stylesheet or XSLT transform (both are discussed in a moment) and automatically display the result to the user instead of the original XML. In this case, the browsers's "view source" feature displays the original XML. One drawback of Mozilla is that it parses large XML documents completely before passing data to the rendering engine, which means that such documents can be slow to load. Mozilla developers have discussed adding incremental XML loading support for several years, but as of 1.5 such capability is not in place. Firefox does not support DTD validation or any of the other validation technologies such as W3C XML Schema (WXS) or RELAX NG. It does support enough of XLink (simple links only) to allow you to express the same sorts of links in XML that you might in HTML. Firefox also supports XML Base, a specification that allows you to set the base URI for resolving relative URIs in XLinks. Links can lead to fragments of documents using the FIXPtr variation on W3C's XPointer or a subset of an older draft of the XPointer specification.
Mozilla Firefox 1.0 supports XHTML 1.0 Strict, Transitional, and Frameset, as well as XHTML 1.1 which is based on modularization of XHTML 1.0 Strict. XHTML 2.0 is still in the working draft stage. Some developers wonder how well XHTML 2.0 will be adopted because it's such a significant change from HTML and XHTML 1.x. I recommend that Web developers targeting Firefox (such as for embedded applications) serve XHTML 1.1. Unfortunately, this may not yet be practical for developers targeting the general Web. I don't intend to discuss XHTML much more in this series, but I do have a full tutorial about XHTML 1.1 on the developerWorks site. (See Resources.)
My colleague, Kurt Cagle, shares his observations about XHTML support:
There are some subtle differences in the layout model of XHTML within Gecko compared to HTML, including the fact that CSS applied to the body only covers the region within the document margins -- to do a full page background, you have to assign the CSS to the
<html>element itself. [Also], Firefox XHTML supports compound document subparts, making it useful to integrate HTML and SVG content, for example.
Cascading Stylesheets (CSS)
Cascading Stylesheets are the prevalent means of rendering XML in a Web browser. Of course, they're also heavily used for HTML style as well, and the technology has always received strong support in Firefox (as in most browsers). CSS 2.0 is a complete recommendation of the W3C, and Firefox 1.0 supports most of the spec. A working draft of CSS 2.1 offers a relatively minor set of revisions to 2.0. CSS 2.0 and 2.1 are collectively called CSS2. Firefox 1.5 improves the CSS2 support and also adds more support for CSS3, which is currently still in working draft stage at the W3C. CSS3 is seeing early adoption because it addresses many pressing needs of Web developers, including better support for XML constructs. Later in the series, I discuss CSS, but I also recommend my series of tutorials (available on developerWorks) about using CSS with XML (see Resources). These resources also include practical demonstration of some of the limitations of Firefox's CSS2 support, most of which is fixed in Firefox 1.5.
Scalable Vector Graphics (SVG)
SVG is the W3C specification providing an XML-based image format. SVG images are portable, resolution-independent, and surprisingly compact -- despite being represented in XML (the result of a few XML design compromises). The feature set includes nested transformations, clipping paths, alpha masks, raster filter effects, template objects, and (of course) extensibility. SVG also supports animation through a module of Synchronized Multimedia Integration Language (SMIL), zooming and panning views, a wide variety of graphic primitives, grouping, scripting, hyperlinks, structured metadata, and easy embedding in other XML documents. SVG works in other XML and Web-related technologies such as CSS and Document Object Model (DOM). Mozilla has had optional and sketchy SVG support for a long while now, but no one put in the effort to get it polished and built-in by default until Firefox 1.5 arrived with out-of-the-box, native SVG support (specifically a subset of SVG 1.1 Full). Some of the features missing in 1.5 are declarative SMIL animation (animation is only possible through scripting), filters, text paths, masks, patterns, and SVG defined fonts. Firefox transparently displays resources served with the MIME-type
image/svg+xml as SVG, with no special plug-ins required; this includes SVG images embedded in
object elements.
MathML is the W3C's XML vocabulary for representing mathematical information. It allows you to express mathematics either with conventions that focus on the abstract mathematical meaning (content markup) or with conventions focused on how it should be displayed (presentation markup). The specification is currently at version 2.0 and Firefox supports this version, either stand-alone or embedded within XHTML. Be warned that users may need to add some fonts to their systems to view MathML documents.
canvas is an element that serves as a scriptable, bitmap drawing surface. The uses are almost endless: games, flashy business presentation graphics, specialized forms controls, simulations, and complex data visualization -- just to name a few possibilities. You define the fixed size of the canvas in the element itself, and then typically you do the actual drawing from a script that uses the canvas API to create visual objects on the canvas. canvas was first developed by Apple for their Safari browser as a foundation for complex graphics facilities such as SVG support. Mozilla picked up the idea, and canvas is now a specification of the WhatWG consortium of browser vendors. Mozilla's canvas currently supports only two-dimensional graphics, but 3D might be on the horizon if OpenGL facilities are made available for the Mozilla platform.
Working the document model
Web browsers have long offered dynamic features so that developers could offer more than simple, static pages. With the trend toward complex Web applications, such features have become even more complex and many of them build on XML in some way. JavaScript (or ECMAScript in its international standard form) is a powerful, dynamic language that forms the basis of most dynamic features in Web browsers.
E4X is a standard that adds native XML datatypes to the ECMAScript language and provides operators for common XML operations. To quote the E4X specification page:.
E4X is probably used most often as a way to parse XML into ECMAScript objects that can be very easily manipulated. This does create some sticky issues because its direct use of XML syntax means it can cause a bit of confusion when embedded in other tag-based formats. In fact, in Firefox 1.5, E4X was disabled by default on HTML pages because it interfered with the traditional way of hiding scripts from noncompatible browsers. However, Web page authors can enable it within any
script element by using an attribute of the form
type="text/javascript; e4x=1".
Mozilla has supported XSLT for nearly five years and in recent years, that support has been fairly reliable, including the ability to invoke XSLT transforms from ECMAScript. Firefox doesn't include any major changes to the workings of XSLT in Mozilla. It would be nice to at least have support for EXSLT extensions, but this is not on the roadmap -- although it has been a topic of discussion and might be a future possibility.
XForms is a specification of Web forms for XML data processing that can be used with a wide variety of platforms through various media. XForms looks to separate a form's purpose from its presentation; that is, what the form does from how it looks. An XML vocabulary can be used to develop form UIs for manipulating XML content. XForms serves as the forms module for XHTML 2.0, but is a stand-alone W3C recommendation. It's more complex than the familiar HTML forms elements, but it can be used to produce much more sophisticated and portable forms. There was some resistance to XForms support in Mozilla because of its complexity, but in August 2004, IBM and Novell offered resources, and the Mozilla Foundation launched a project to implement XForms in Mozilla. The fruit of this labor is available in Firefox as an extension. Firefox also adds support for XML Events, a W3C specification, related to XForms, for listening for events related to the manipulation of XML objects, and for handling such events. As an example, an XML event would be raised when a user changes the text in an XForms-based text entry field.
eXtensible Tag Framework (XTF)
XTF is a Mozilla-specific technology that allows extension authors to create new XML namespaces in Mozilla, using code that they write in ECMAScript or C++ (technically, they can write in any language with support for the Mozilla component system, XPCOM). In fact, XTF is what the Mozilla XForms Project uses to add support for elements in the XForms namespace. XTF promises to be a powerful way to add all sorts of XML technologies to Mozilla without having to wait for support in the core.
Firefox allows you to access XML Web services from ECMAScript. There are components for SOAP 1.1, WSDL 1.1, and XML-RPC. In this way, you can incorporate features that are available through messages from remote service providers.
Firefox: The complete XML-based browser workbench
For some people, the crown jewel of Mozilla's XML capabilities is XML User Interface Language (XUL), a markup language for describing cross-platform user interfaces. XUL is designed for the Mozilla platform but intended for more general use. The best way to think about XUL is to imagine all the various bits and pieces that appear in a Web browser: a main rendering area, menus, icons and buttons, a URL bar, title bars, status bars, sidebars, dialog boxes, and so forth. XUL allows you to create, arrange, and activate all these components. In fact, the full Mozilla Web browser was written as an XUL application. An XUL application is specified in XML where each component is defined. Firefox 1.5 brings some important enhancements to XUL, including dynamic overlays and translucent backgrounds, which increases your flexibility in combining and presenting XUL components. XUL works closely with another XML-based declaration language, Extensible Binding Language (XBL), which allows you to specify special behavior for components expressed in XUL. Mozilla also uses Resource Description Framework (RDF) to manage semi-structured data used in XUL. RDF is a metadata system with an XML serialization for the Web, a model for describing collections of formalized statements about a Web resource.
You can see how broad and deep Firefox's XML support is. In this article, you viewed a high-altitude map of these features. In forthcoming articles, you'll get more detail about much of this territory, with snippets of working code for Firefox. This is a particularly exciting time for XML developers since XML is driving the next generation of Web technology, and Firefox users stand poised to take advantage of these developments.
Thanks to Kurt Cagle, for providing assistance with this article.
Learn
- If you want to keep an eye on the development of Firefox beyond 1.5, the best source is the Firefox roadmap page.
- Many of the XML technologies mentioned in this article are covered in "A survey of XML standards: Part 4," by Uche Ogbuji (developerWorks, March 2004), which provides a detailed cross reference of the most important XML standards.
- Read about IBM's adoption of Firefox and the more general initiative for increasing Firefox adoption at Spread Firefox.
- Learn about SVG from the tutorial "Introduction to Scalable Vector Graphics," by Nicholas Chase (developerWorks, March 2004), which provides many examples. Find out more about SVG in Mozilla (and thus Firefox) in the Mozilla SVG FAQ. If you really want the in-depth details, check out the Mozilla SVG Status page.
- Learn about MathML from "A Gentle Introduction to MathML," by Robert Miner and Jeff Schaeffer. If interested, go on to "MathML: Presenting and Capturing Mathematics for the Web (PDF)," by Michael Kohlhase for greater depth. Learn about Mozilla's implementation on the project page, but be aware that this page is out of date.
- See the announcement of the Mozilla/XForms project.
- Check out the XTF project page to learn about this new capability that allows you to create an extension to handle whatever XML you like.
- Read more about canvas at the Mozilla Developer Center: Drawing Graphics with Canvas.
- Learn more about XUL, XBL, and how RDF is used in Mozilla.
- Find more XML resources on the developerWorks XML zone. If you're looking for more about Web-related technologies, check out the Web architecture zone.
- Find out how you can become an IBM Certified Developer in XML and related technologies.
- Refer to the W3C HTML Home Page for information about all versions of XHTML. Uche Ogbuji's developerWorks tutorial "XHTML, step by step" (September 2005) is another great place to get started with the technology.
- Take a closer look at Cascading Stylesheets. Read Uche Ogbuji's three-part tutorial series "Use Cascading Stylesheets to display XML":
- Part 1 (November 2004) shows you how to use CSS to display XML in browsers.
- Part 2 (February 2005) builds on the basics in Part 1 to cover more intermediate and advanced topics.
- Part 3 (June 2005) covers techniques for using XSLT to process XML in association with CSS.
Get products and technologies
- Get Firefox, the Mozilla-based Web browser that offers standards compliance, performance, security, and solid XML features.
> find more about Mr. Ogbuji at his Weblog Copia or contact him at uche@ogbuji.net. | http://www.ibm.com/developerworks/xml/library/x-ffox15.html | crawl-002 | refinedweb | 2,785 | 53.1 |
ok i dont know how to do error handling. i was hoping there was a place i can learn that... can anyone point me to the right place?
ok i dont know how to do error handling. i was hoping there was a place i can learn that... can anyone point me to the right place?
Last edited by Panzer_online; 04-24-2004 at 06:57 AM.
if u c this i will be asking for help
>ok i dont know how to do error handling.
Error handling is application specific. As long as you check your return values and initialize your variables properly you'll have done the majority of the work. Past that it's all about how you react to an error.
Most simple programs will just bail when something unexpected happens, but for larger programs you will need to perform some form of recovery. However, this usually isn't possible at the location that the error occurs, so a good way to move up the call chain to get to a place that is prepared to handle your error would be using exceptions.
Any good book on C++ will give you more detail than I can here on exceptions, but the idea is like this (off the top of my head):
Code:#include <cstdlib> #include <iostream> #include <new> using namespace std; namespace { const int MAX_RECOVERY = 10; size_t recovery_index; int recovery[MAX_RECOVERY]; } int main() { for ( int i = 0; i < 20; i++ ) { int *p; bool recover = false; try { throw bad_alloc(); p = new int; recover = false; } catch ( bad_alloc& ) { if ( recovery_index == MAX_RECOVERY ) { cerr<<"Memory exhausted, no recovery available\n"; return EXIT_FAILURE; } else { int recovery_left = sizeof *recovery * (MAX_RECOVERY - recovery_index - 1); cerr<<"Memory exhausted, recovery available: "<< recovery_left <<" bytes\n"; p = &recovery[recovery_index++]; } recover = true; } *p = i; cout<< *p <<endl; if ( !recover ) { delete p; } } }
My best code is written with the delete key.
Well I have my handy dandy 900 page book about C++ here.........hmm.......ah........here we are the chapter on exceptions.
Lemme see if I can nitpick Prelude's code.
....posts to follow I'm sure.
ROFL.
hmmm.... ok.. well... i kinder get most of that.. but if i have an int and i put in a char it goes crazy.... how (or point me to the place) would i fix that?
if u c this i will be asking for help | https://cboard.cprogramming.com/cplusplus-programming/52146-need-help-have-done-c-befor-new-cplusplus.html | CC-MAIN-2017-13 | refinedweb | 392 | 71.85 |
LoPy4 failing to connect to Australia TTN?
- Victor Hooi last edited by
I have purchased several LoPy4 kits, and I'm trying to connect them to the local TTN network here in Australia.
First, I followed the tutorial at to register the LoPy4 device on TTN.
- I created a new application.
- I selected "Add end device". PyCom/LoPy didn't appear in the "LoRaWAN device repository", so I picked "Manually"
- LoRaWAN verison was set to "MAC V1.0.2"
- Regional Parameters version was set to "PHY V1.0.2 REV A"
- Frequency Plan was set to "Australia 915-928 MHz, FSB 2 (used by TTN)"
- I got my DevEUI from the LoPy4 using the below snippet:
from network import LoRa import ubinascii lora = LoRa() print("DevEUI: %s" % (ubinascii.hexlify(lora.mac()).decode('ascii')))
- AppEUI was filled with zeros
- AppKey was generated
- End Device ID was pre-filled with the DevEUI - I left this alone.
I then tried to register the device to the network via OTAA, using some of the commands from.
>>> from network import LoRa >>> import socket >>> import time >>> import ubinascii >>> lora = LoRa(mode=LoRa.LORAWAN, region=LoRa.AU915) >>> dev_eui = ubinascii.unhexlify('SANITISED') >>> app_eui = ubinascii.unhexlify('0000000000000000') >>> app_key = ubinascii.unhexlify('SANITISED') >>> lora.join(activation=LoRa.OTAA, auth=(dev_eui, app_eui, app_key), timeout=0)
I then wait several minutes to see if it's joined - and it hasn't:
>>> lora.has_joined() False
Does anybody have any ideas why it's failing to connect?
Also, from the official LoRaWAN OTAA instructions, there's two points that aren't very clear:
- It's unclear when you should specify
dev_euior when you should let is use the default? When would you use one over the other?
-.
@GregS Caution: I now believe that the only reason that code works for me is because it uses DR0 for the join requests, which is in violation of the regional parameters for Australia, which say to use DR2. I.e - I am too far away from a gateway. As I have said in another thread, the proper way of joining using OTAA is actually working for me, when get closer.
(I don't know WHY that code uses DR0, but I don't really care - it's not code I will be using any more)
FWIW, I've managed to get my LoPy 1 (running current FW) to join using OTAA, using this rather old code:
I don't know how reliable it is yet - all I have done is the join.
- Gijs Global Moderator last edited by
@jcaron in the new TTN (nowadays called The Things Stack) they no longer provide a random app EUI, so you'll have to make up your own. Their instructions mention to use all 0's.
Indeed check if you're in range of a local gateway..
The frequency plan FSB2 indeed coincides with the instructions listed in the green block on this page:: long story short, a gateway generally listens to only 8 channels, of which these 8 are the most common, and listed on the TTS as 'FSB2'. The instructions mention Pygate, but with the new TTS interface, it is possible to define the frequency plan in more detail than before.
# Uncomment for US915 / AU915 & Pygate # for i in range(0,8): # lora.remove_channel(i) # for i in range(16,65): # lora.remove_channel(i) # for i in range(66,72): # lora.remove_channel(i)
concerning your other question
It's unclear when you should specify dev_eui or when you should let is use the default? When would you use one over the other?
The only requirement is that the
dev_euiis both the same on the device and in TTS. In some cases its convenient to use the LoRa MAC of the Lopy4, in other cases its convenient to use the TTS provided value.
I've never got an OTAA join confirmation here in AU for pycom devices. Give ABP a shot that seemed to work.
@Victor-Hooi the all-zeroes App EUI seems weird to me, although I haven’t used the TTN UI in a long time.
Are you within reach of an existing gateway? Are you indoors or outdoors? Do you have line of sight? how far away are you? Do you know the details of the gateway?
IIRC the AU frequency plan is similar to the US plan, having a lot more channels than a single gateway can support, so you need to remove a lot of channels and only keep those actually used by the network, that’s probably the commented parts you are referring to. | https://forum.pycom.io/topic/7196/lopy4-failing-to-connect-to-australia-ttn | CC-MAIN-2022-05 | refinedweb | 760 | 63.59 |
One of the most popular ES6 features is object and array destructuring. Destructuring is the process of taking specific elements from an array or properties from an object and then turning them into variables. While it's not essential to incorporate this feature in our projects right now, it's a useful convenience. Object destructuring is very common in React, so even if you don't use it much now, it will come up again once we start working with React. You will not be expected to incorporate destructuring for this section's independent project. However, you should recognize destructuring out in the wild - and give it a whirl in your projects if you can.
Let's say we have an array of numbers that looks like this:
const numArray = [1, 2, 3];
To get elements from the array and assign them to variables, we might do something like this:
const firstElement = numArray[0]; const secondElement = numArray[1]; const thirdElement = numArray[2];
We can make this process much simpler with array destructuring:
const [firstElement, secondElement, thirdElement] = numArray;
In this example, we are destructuring the elements of the array into variables.
firstElement corresponds to the first element of the array,
secondElement corresponds to the second element, and so on.
Try this out in the console and check the values of each of the variables.
We've reduced three lines of code to one.
We don't have to destructure the entire array. For instance, if we just need the first element, we could do this:
const [firstElement] = numArray;
The
firstElement variable is now set to the first element in
numArray - but there is no
secondElement or
thirdElement.
Object destructuring is both more useful and more common. We can use it to assign specific properties of an object to variables. Here's an example:
const obj = { color1: "red", color2: "blue", color3: "yellow", description: "Information we don't need", anotherProp: "We don't need this info, either" };
Let's say we just want to get the colors from this object. We can destructure them like this:
const { color1, color2, color3 } = obj;
In this example, we are pulling out the properties from the object and saving them as constants with the same names.
Try it in the console:
color1; > "red" color2; > "blue" color3; > "yellow"
Since we've only destructured the colors, we don't have equivalent variables for
description or
anotherProp.
Let's say we want to take this one step further and create a variable for a property - but the variable should have a different name from the original property. We can do this:
const { color1: red, color2: blue } = obj;
Now we have variables for
red (which corresponds to the
color1 property) and
blue (which corresponds to the
color2 property). Note that there is no
color1 or
color2 variable because we chose different names for the variables.
By the way, the syntax for object destructuring should already look familiar from the import statements we've used with named exports. For instance, as we discussed in the ES6 Imports and Exports lesson, we can do the following:
import { Triangle, Rectangle, Circle } from './shapes.js';
As we can see, import statements that are used with named exports use this destructuring syntax as well.
This lesson covers the basics of array and object destructuring but there are plenty of other things we can do with destructuring, too. Check out the Mozilla documentation on Destructuring Assignment to learn more.
Lesson 40 of 48
Last updated April 8, 2021 | https://www.learnhowtoprogram.com/intermediate-javascript/test-driven-development-and-environments-with-javascript/destructuring-arrays-and-objects | CC-MAIN-2021-17 | refinedweb | 581 | 58.01 |
:
I don't think I've seen this issue before... Do you have some error in your
error log? (See:)
Also, not sure if you've read the session related to running a program in the
getting started guide: (I know you work
in PyDev for quite some time, but if you haven't read it, it might be worth
it -- you can rebind the bindings cited in that page if you want).
Cheers,
Fabio
The following forum message was posted by jgver at:
In one of the last few PyDev updates, I've noticed that launch configurations
disappear. Every time I try to run a script, using F5 (I'm using the Visual
Studio key configuration scheme), PyDev will ask me if I want to debug as "Python
Run" or "Python unit-test". I get this dialog every time I run a script. Prior
to a few weeks ago, I would only have to do this once, and then all subsequent
launches would use the previous launch configuration.
And if I go to the launch configuration dialog ("Run/Debug Settings" from the
Properties dialog for a given Python file), no launch configurations appear.
If I try to create a new launch configuration using the Project's name and the
Python file's name appended to it (which is how PyDev automatically names them),
I get an error saying that a launch configuration with that name already exists.
This behavior has just started happening a few weeks ago. (I've been using
PyDev for almost 3 years). Is this a bug, or has handling of launch configurations
changed recently?
Thanks in advance,
Jeff
The following forum message was posted by jgver at:
Thanks for the help! I think this might be a case of an eclipse workspace that
has been around for years, has had many projects in it (some used for actual
development, others just test projects) survived several updates of both PyDev
and Eclipse, and has generally just gotten too big for its britches. I removed
a lot of the old (and unused) projects, and created a new launch configuration
for my current project, and that one behaves normally.
[quote]Also, not sure if you've read the session related to running a program
in the getting started guide:[/quote]
Good stuff! It's never too late for this old dog to learn some new tricks!
:-) I set the preference, "Always launch the previously launched application"
and now F5 runs the previous launch config. Yay!
Thanks for your help!
Jeff
The following forum message was posted by tsemple at:
I am experiencing a variation of this problem. In my case it applies only to
one of my PyDev projects. I can fill out a launch configuration and use
it successfully one time (or re-run during that session), but it never again
appears in the Run Configurations list. The launch configuration files exist
in my workspace (in .metadata/plugins/org.eclipse.debug.core/.launches) but
they seem to be filtered out somewhere along the way, I assume by Pydev. Meanwhile
other PyDev projects (and Java projects) do not have this problem.
I've tried recreating the project from scratch, and was able to have a configuration
'stick' one time, but it vanished after some perspective change or close of
the project, never to return (after opening the project again).
Most annoying.". | https://sourceforge.net/p/pydev/mailman/message/27726368/ | CC-MAIN-2018-09 | refinedweb | 563 | 58.82 |
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Hi,
We have a large code base which uses WinSock calls and these appear to be available to runtime apps (as highlighted here:). Great news.
However we also would like our app to have a long-lived network connection so I've been looking into using ControlChannelTrigger. This would appear to be what we want to talk to a legacy server, albeit with the requirement that the user approves our
app for the lock screen.
So is it possible to use ControlChannelTrigger and old-style sockets? ControlChannelTrigger only appears to take StreamSockets or IXMLHTTPRequest (our socket communication isn't HTTP based).
If not has anyone else solved this issue?
All help greatly appreciated.
Thanks
No, you cannot use winsock API with ControlChannelTrigger. In fact, you can only use the Windows Runtime Networking API that is available in the Windows.Networking.Sockets namespace. For example: StreamSocket for TCP Socket and DatagramSocket for
UDP socket.
The Desktop Winsock functionality cannot be used in Windows Runtime apps. See the documentation for socket/connect/send/recv/closesocket and notice that it says "Desktop apps only"
Windows Store Developer Solutions, follow us on Twitter:
@WSDevSol|| Want more solutions? See our blog | https://social.msdn.microsoft.com/Forums/en-US/e20781d7-d837-4a10-bfc3-ae9ed3ea96d0/controlchanneltrigger-and-winsock?forum=winappswithnativecode | CC-MAIN-2018-51 | refinedweb | 198 | 56.76 |
It can be useful to artificially tint an image with some color, either to highlight particular regions of an image or maybe just to liven up a grayscale image. This example demonstrates image-tinting by scaling RGB values and by adjusting colors in the HSV color-space.
In 2D, color images are often represented in RGB—3 layers of 2D arrays, where the 3 layers represent (R)ed, (G)reen and (B)lue channels of the image. The simplest way of getting a tinted image is to set each RGB channel to the grayscale image scaled by a different multiplier for each channel. For example, multiplying the green and blue channels by 0 leaves only the red channel and produces a bright red image. Similarly, zeroing-out the blue channel leaves only the red and green channels, which combine to form yellow.
import matplotlib.pyplot as plt from skimage import data from skimage import color from skimage import img_as_float grayscale_image = img_as_float(data.camera()[::2, ::2]) image = color.gray2rgb(grayscale_image) red_multiplier = [1, 0, 0] yellow_multiplier = [1, 1, 0] fig, (ax1, ax2) = plt.subplots(ncols=2, figsize=(8, 4), sharex=True, sharey=True) ax1.imshow(red_multiplier * image) ax2.imshow(yellow_multiplier * image)
In many cases, dealing with RGB values may not be ideal. Because of that, there are many other color spaces in which you can represent a color image. One popular color space is called HSV, which represents hue (~the color), saturation (~colorfulness), and value (~brightness). For example, a color (hue) might be green, but its saturation is how intense that green is —where olive is on the low end and neon on the high end.
In some implementations, the hue in HSV goes from 0 to 360, since hues wrap around in a circle. In scikit-image, however, hues are float values from 0 to 1, so that hue, saturation, and value all share the same scale.
Below, we plot a linear gradient in the hue, with the saturation and value turned all the way up:
import numpy as np hue_gradient = np.linspace(0, 1) hsv = np.ones(shape=(1, len(hue_gradient), 3), dtype=float) hsv[:, :, 0] = hue_gradient all_hues = color.hsv2rgb(hsv) fig, ax = plt.subplots(figsize=(5, 2)) # Set image extent so hues go from 0 to 1 and the image is a nice aspect ratio. ax.imshow(all_hues, extent=(0, 1, 0, 0.2)) ax.set_axis_off()
Notice how the colors at the far left and far right are the same. That reflects the fact that the hues wrap around like the color wheel (see HSV for more info).
Now, let’s create a little utility function to take an RGB image and:
1. Transform the RGB image to HSV 2. Set the hue and saturation 3. Transform the HSV image back to RGB
def colorize(image, hue, saturation=1): """ Add color of the given hue to an RGB image. By default, set the saturation to 1 so that the colors pop! """ hsv = color.rgb2hsv(image) hsv[:, :, 1] = saturation hsv[:, :, 0] = hue return color.hsv2rgb(hsv)
Notice that we need to bump up the saturation; images with zero saturation are grayscale, so we need to a non-zero value to actually see the color we’ve set.
Using the function above, we plot six images with a linear gradient in the hue and a non-zero saturation:
hue_rotations = np.linspace(0, 1, 6) fig, axes = plt.subplots(nrows=2, ncols=3, sharex=True, sharey=True) for ax, hue in zip(axes.flat, hue_rotations): # Turn down the saturation to give it that vintage look. tinted_image = colorize(image, hue, saturation=0.3) ax.imshow(tinted_image, vmin=0, vmax=1) ax.set_axis_off() fig.tight_layout()
You can combine this tinting effect with numpy slicing and fancy-indexing to selectively tint your images. In the example below, we set the hue of some rectangles using slicing and scale the RGB values of some pixels found by thresholding. In practice, you might want to define a region for tinting based on segmentation results or blob detection methods.
from skimage.filters import rank # Square regions defined as slices over the first two dimensions. top_left = (slice(100),) * 2 bottom_right = (slice(-100, None),) * 2 sliced_image = image.copy() sliced_image[top_left] = colorize(image[top_left], 0.82, saturation=0.5) sliced_image[bottom_right] = colorize(image[bottom_right], 0.5, saturation=0.5) # Create a mask selecting regions with interesting texture. noisy = rank.entropy(grayscale_image, np.ones((9, 9))) textured_regions = noisy > 4 # Note that using `colorize` here is a bit more difficult, since `rgb2hsv` # expects an RGB image (height x width x channel), but fancy-indexing returns # a set of RGB pixels (# pixels x channel). masked_image = image.copy() masked_image[textured_regions, :] *= red_multiplier fig, (ax1, ax2) = plt.subplots(ncols=2, nrows=1, figsize=(8, 4), sharex=True, sharey=True) ax1.imshow(sliced_image) ax2.imshow(masked_image) plt.show()
For coloring multiple regions, you may also be interested in skimage.color.label2rgb.
Total running time of the script: ( 0 minutes 0.431 seconds)
Gallery generated by Sphinx-Gallery | https://scikit-image.org/docs/stable/auto_examples/color_exposure/plot_tinting_grayscale_images.html | CC-MAIN-2019-18 | refinedweb | 829 | 57.47 |
Azure Relay FAQs
This article answers some frequently asked questions (FAQs) about Azure Relay. For general Azure pricing and support information, see Azure Support FAQs.
General questions
What is Azure Relay?
The Azure Relay service facilitates your hybrid applications by helping you more securely expose services that reside within a corporate enterprise network to the public cloud. You can expose the services without opening a firewall connection, and without requiring intrusive changes to a corporate network infrastructure.
What is a Relay namespace?
A namespace is a scoping container that you can use to address Relay resources within your application. You must create a namespace to use Relay. This is one of the first steps in getting started.
What happened to Service Bus Relay service?
The previously named Service Bus Relay service is now called WCF Relay. You can continue to use this service as usual. The Hybrid Connections feature is an updated version of a service that's been transplanted from Azure BizTalk Services. WCF Relay and Hybrid Connections both continue to be supported.
This section answers some frequently asked questions about the Relay pricing structure. You also can see Azure Support FAQs for general Azure pricing information. For complete information about Relay pricing, see Service Bus pricing details.
How do you charge for Hybrid Connections and WCF Relay?
For complete information about Relay pricing, see the Hybrid Connections and WCF Relays table on the Service Bus pricing details page. In addition to the prices noted on that page, you are charged for associated data transfers for egress outside of the datacenter in which your application is provisioned.
How am I billed for Hybrid Connections?
Here are three example billing scenarios for Hybrid Connections:
- Scenario 1:
- You have a single listener, such as an instance of the Hybrid Connections Manager installed and continuously running for the entire month.
- You send 3 GB of data across the connection during the month.
- Your total charge is $5.
- Scenario 2:
- You have a single listener, such as an instance of the Hybrid Connections Manager installed and continuously running for the entire month.
- You send 10 GB of data across the connection during the month.
- Your total charge is $7.50. That's $5 for the connection and first 5 GB + $2.50 for the additional 5 GB of data.
- Scenario 3:
- You have two instances, A and B, of the Hybrid Connections Manager installed and continuously running for the entire month.
- You send 3 GB of data across connection A during the month.
- You send 6 GB of data across connection B during the month.
- Your total charge is $10.50. That's $5 for connection A + $5 for connection B + $0.50 (for the sixth gigabyte on connection B).
Note that the prices used in the examples are applicable only during the Hybrid Connections preview period. Prices are subject to change upon general availability of Hybrid Connections.
How are hours calculated for Relay?
WCF Relay is available only in Standard tier namespaces. Pricing and connection quotas for relays otherwise have not changed. This means that relays continue to be charged based on the number of messages (not operations) and relay hours. For more information, see the "Hybrid Connections and WCF Relays" table on the pricing details page.
What if I have more than one listener connected to a specific relay?
In some cases, a single relay might have multiple connected listeners. A relay is considered open when at least one relay listener is connected to it. Adding listeners to an open relay results in additional relay hours. The number of relay senders (clients that invoke or send messages to relays) that are connected to a relay does not affect the calculation of relay hours.
How is the messages meter calculated for WCF Relays?
(This applies only to WCF relays. Messages are not a cost for Hybrid Connections.)
In general, billable messages for relays are calculated by using the same method that is used for brokered entities (queues, topics, and subscriptions), described previously. However, there are some notable differences.
Sending a message to a Service Bus relay is treated as a "full through" send to the relay listener that receives the message. It is not treated as a send operation to the Service Bus relay, followed by a delivery to the relay listener. A request-reply style service invocation (of up to 64 KB) against a relay listener results in two billable messages: one billable message for the request and one billable message for the response (assuming the response is also 64 KB or smaller). This is different than using a queue to mediate between a client and a service. If you use a queue to mediate between a client and a service, the same request-reply pattern requires a request send to the queue, followed by a dequeue/delivery from the queue to the service. This is followed by a response send to another queue, and a dequeue/delivery from that queue to the client. Using the same size assumptions throughout (up to 64 KB), the mediated queue pattern results in 4 billable messages. You'd be billed for twice the number of messages to implement the same pattern that you accomplish by using relay. Of course, there are benefits to using queues to achieve this pattern, such as durability and load leveling. These benefits might justify the additional expense.
Relays that are opened by using the netTCPRelay WCF binding treat messages not as individual messages, but as a stream of data flowing through the system. When you use this binding, only the sender and listener have visibility into the framing of the individual messages sent and received. For relays that use the netTCPRelay binding, all data is treated as a stream for calculating billable messages. In this case, Service Bus calculates the total amount of data sent or received via each individual relay on a 5-minute basis. Then, it divides that total amount of data by 64 KB to determine the number of billable messages for that relay during that time period.
Quotas
Does Relay have any usage quotas?
By default, for any cloud service, Microsoft sets an aggregate monthly usage quota that is calculated across all of a customer's subscriptions. We understand that at times your needs might exceed these limits. You can contact customer service at any time, so we can understand your needs and adjust these limits appropriately. For Service Bus, the aggregate usage quotas are as follows:
- 5 billion messages
- 2 million relay hours
Although we reserve the right to disable an account that exceeds its monthly usage quotas, we provide e-mail notification, and we make multiple attempts to contact the customer before taking any action. Customers that exceed these quotas are still responsible for excess charges.
Naming restrictions
A Relay namespace name must be between 6 and 50 characters in length.
Subscription and namespace management
How do I migrate a namespace to another Azure subscription?
To move a namespace from one Azure subscription to another subscription, you can either use the Azure portal or use PowerShell commands. To move a namespace to another subscription, the namespace must already be active. The user running the commands must be an Administrator user on both the source and target subscriptions.
Azure portal
To use the Azure portal to migrate Azure Relay namespaces from one subscription to another subscription, see Move resources to a new resource group or subscription.
PowerShell
To use PowerShell to move a namespace from one Azure subscription to another subscription, use the following sequence of commands. To execute this operation, the namespace must already be active, and the user running the PowerShell commands must be an Administrator user on both the source and target subscriptions.
# Create a new resource group in the target subscription. Select-AzureRmSubscription -SubscriptionId 'ffffffff-ffff-ffff-ffff-ffffffffffff' New-AzureRmResourceGroup -Name 'targetRG' -Location 'East US' # Move the namespace from the source subscription to
Troubleshooting
What are some of the exceptions generated by Azure Relay APIs, and suggested actions you can take?
For a description of common exceptions and suggested actions you can take, see Relay exceptions.
What is a shared access signature, and which languages can I use to generate a signature?
Shared Access Signatures (SAS) are an authentication mechanism based on SHA-256 secure hashes or URIs. For information about how to generate your own signatures in Node, PHP, Java, C, and C#, see Service Bus authentication with shared access signatures.
Is it possible to whitelist relay endpoints?
Yes. The relay client makes connections to the Azure Relay service by using fully qualified domain names. Customers can add an entry for
*.servicebus.windows.net on firewalls that support DNS whitelisting. | https://docs.microsoft.com/en-us/azure/service-bus-relay/relay-faq | CC-MAIN-2018-13 | refinedweb | 1,452 | 55.54 |
import "crypto/ed25519"
Package ed25519 implements the Ed25519 signature algorithm. See.
These functions are also compatible with the “Ed25519” function defined in
RFC 8032. However, unlike RFC 8032's formulation, this package's private key
representation includes a public key suffix to make multiple signing
operations with the same key more efficient. This package refers to the RFC
8032 private key as the “seed”.
ed25519.go
const (
// PublicKeySize is the size, in bytes, of public keys as used in this package.
PublicKeySize = 32
// PrivateKeySize is the size, in bytes, of private keys as used in this package.
PrivateKeySize = 64
// SignatureSize is the size, in bytes, of signatures generated and verified by this package.
SignatureSize = 64
// SeedSize is the size, in bytes, of private key seeds. These are the private key representations used by RFC 8032.
SeedSize = 32
)
func GenerateKey(rand io.Reader) (PublicKey, PrivateKey, error)
GenerateKey generates a public/private key pair using entropy from rand.
If rand is nil, crypto/rand.Reader will be used.
func Sign(privateKey PrivateKey, message []byte) []byte
Sign signs the message with privateKey and returns a signature. It will
panic if len(privateKey) is not PrivateKeySize.
func Verify(publicKey PublicKey, message, sig []byte) bool
Verify reports whether sig is a valid signature of message by publicKey. It
will panic if len(publicKey) is not PublicKeySize.
PrivateKey is the type of Ed25519 private keys. It implements crypto.Signer.
type PrivateKey []byte
func NewKeyFromSeed(seed []byte) PrivateKey
NewKeyFromSeed calculates a private key from a seed. It will panic if
len(seed) is not SeedSize. This function is provided for interoperability
with RFC 8032. RFC 8032's private keys correspond to seeds in this
package.
func (priv PrivateKey) Public() crypto.PublicKey
Public returns the PublicKey corresponding to priv.
func (priv PrivateKey) Seed() []byte
Seed returns the private key seed corresponding to priv. It is provided for
interoperability with RFC 8032. RFC 8032's private keys correspond to seeds
in this package.
func (priv PrivateKey) Sign(rand io.Reader, message []byte, opts crypto.SignerOpts) (signature []byte, err error)
Sign signs the given message with priv.
Ed25519 performs two passes over messages to be signed and therefore cannot
handle pre-hashed messages. Thus opts.HashFunc() must return zero to
indicate the message hasn't been hashed. This can be achieved by passing
crypto.Hash(0) as the value for opts.
PublicKey is the type of Ed25519 public keys.
type PublicKey []byte | https://golang.org/pkg/crypto/ed25519/ | CC-MAIN-2020-05 | refinedweb | 402 | 61.22 |
I have spent the evening trying to complete a program to be turned in before midnight. This program simulates the game Rock, Paper, Scissors. Towards the end of the code, I had thrown in the if-statments declaring 1 = rock, etc. I can't find my last mistake. Any advice guys?
BTW: I am using Dev C++ Compiler from Bloodshed.
//Kerri Byrd //August 2, 2004 //C14A3P779 #include <iostream> #include <cstdlib> #include <conio.h> using namespace std; int main () { int computerWins = 0; int myWins = 0; int ties = 0; int turns = 0; unsigned int computerChoice = 0; int myChoice = 0; srand ((unsigned) time (NULL)); computerChoice = rand() % 4; cout << "Enter your choice: " << endl; cin >> myChoice; cout << "Computer's Choice " <<computerChoice << endl; { if (myChoice > computerChoice) { myWins = myWins + 1; } else computerWins = computerWins + 1; } if (myChoice == computerChoice) { ties = ties + 1; } cout << "My Wins " << myWins << endl; cout << "Computer's Wins " << computerWins << endl; cout << "Ties " << ties << endl; getch (); return 0; } if (myChoice || computerChoice == 1) { cout << "Rock "; } else if (myChoice || computerChoice == 2) { cout << "Paper "; } else if (myChoice || computerChoice ==3) { cout << "Scissors"; }
<< moderator edit: added code tags: [code][/code] >> | https://www.daniweb.com/programming/software-development/threads/29673/i-need-a-bit-of-help-asap | CC-MAIN-2017-26 | refinedweb | 178 | 58.11 |
On Thu, 2009-04-23 at 07:56 -0500, Bob Gustafson wrote: > On Apr 23, 2009, at 07:47, James Laska wrote: > > >. > > > > They look good, thanks Liam. I've made a few corrections including > > moving into the QA: wiki namespace and utilizing the {{QA/Test_Case}} > > template. I've only updated > > QA:Testcase_Anaconda_Upgrade_New_Bootloader > > to the new template, you may wish to do the same for the others. > > > > We don't have a section related to upgrades in the Fedora 11 > > installation test matrix, would it make sense to add your new tests to > >? > > > > Thanks, > > James > > > > It might be good to add test cases for upgrading to ext4 from ext3 too. I've not tested this explicitly yet. Are there certain prompts for that the user must acknowledge/respond? Does anaconda automatically upgrade non-/boot ext3 partitions to ext4 during an upgrade? If you've recently performed an anaconda upgrade like this, I'd be interested in your experiences. Thanks, James -- ========================================== James Laska -- jlaska redhat com Quality Engineering -- Red Hat, Inc. ==========================================
Attachment:
signature.asc
Description: This is a digitally signed message part | https://www.redhat.com/archives/fedora-test-list/2009-April/msg01497.html | CC-MAIN-2017-51 | refinedweb | 180 | 57.47 |
Issue Type: Bug Created: 2009-06-09T00:50:12.000+0000 Last Updated: 2009-08-03T05:18:44.000+0000 Status: Resolved Fix version(s): - 1.9.0 (31/Jul/09)
Reporter: Weber Chris (chrisweb) Assignee: Ben Scholzen (dasprid) Tags: - Zend_Config
Related issues: Attachments: - patch.patch
Its its not possible to use constants in the config xml, for example APPLICATION_PATH, to configure for example resources
for example this works in ini files:
bootstrap.path = APPLICATION_PATH "/Bootstrap.php"
but in config xml it doesnt
APPLICATION_PATH "/Bootstrap.php"
Posted by Florent Cailhol (ooflorent) on 2009-06-11T03:23:43.000+0000
Actualy, when using an ini file, parse_ini_file() is used. This function handles PHP constants contrary to simplexml_load_file() which does not. In order to add the constant support in Zend_Application when using xml files, Zend_Config_Xml must be rewrite.
Posted by julien PAULI (doctorrock83) on 2009-06-12T12:50:29.000+0000
That patch could make it. Let's Rob review it ;-)
Posted by julien PAULI (doctorrock83) on 2009-06-12T12:54:38.000+0000
Mind there is a typo in the patch , replace $this->_parseXMl() by $this->_parseXmlForPHPConstants() ; forgot to rename it.
Posted by Rob Allen (rob) on 2009-06-16T03:41:48.000+0000
-Will have a look soon. Ping me if I don't come back within a week!-
Update: looked!
Problem with patch is that it doesn't prevent constants in tag names and doesn't seem to handle concatenating constants within a string.
Posted by Ben Scholzen (dasprid) on 2009-06-16T03:47:56.000+0000
Imho that's not the way to go. I spoke with SpotSec about it already, and we think that you should include a namespace for inserting constants, so for example:
<pre class="highlight"> /Bootstrap.php
Posted by Ryan Mauger (bittarman) on 2009-06-16T03:59:10.000+0000
+1 for Bens suggestion.
This could also be used for further features later, such as XML includes (if it is decided to support them), and would add a consistend interface for such things.
Posted by Rob Allen (rob) on 2009-06-16T03:59:25.000+0000
I quite like Ben & SpotSec's proposal on the grounds that it is completely backwards compatible.
Also, we should put extends within the namespace for the future and check with Matthew about the namespace to use.
Finally, I'd like to see the patch :)
Posted by Ben Scholzen (dasprid) on 2009-06-16T07:20:26.000+0000
Partly patch to fix the issue. Not all unit tests included yet, no support for namespace:extends, no documentation. Will be finished and comitted to trunk after Rob reviewed it.
Posted by Rob Allen (rob) on 2009-06-21T12:13:11.000+0000
Patch looks okay to me.
Have pinged Matthew to a-okay the concept and URI before we go ahead and implement.
Posted by Geoffrey Tran (potatobob) on 2009-06-21T13:43:02.000+0000
A namespace would simply be "" etc..., but it might be nice if "zf" was the default
</path,>
Posted by Lex Viatkin (viatkine) on 2009-06-28T16:09:03.000+0000
"Now, create your configuration. For this tutorial, we will use an INI style configuration; you may, of course, use an XML or PHP configuration file as well."
Please, remove this part from documentation until this issue will be fixed. I spent 1 hour to find out "why my XML config doesnt work.. they say it have!"…
Posted by Aron Rotteveel (arondeparon) on 2009-07-01T03:05:15.000+0000
Is there any ETA on when this feature will be released? I just discovered about this and would definately like to see this happening soon.
Posted by Ben Scholzen (dasprid) on 2009-07-01T03:15:56.000+0000
I'm waiting for Matthew's okay and will then finish it.
Posted by Rob Allen (rob) on 2009-07-21T14:29:12.000+0000
For reference, resolved in svn 16924
Posted by Weber Chris (chrisweb) on 2009-08-03T05:18:44.000+0000
Thx a lot for resolving this issue, great job! | https://framework.zend.com/issues/browse/ZF-6960?focusedCommentId=31874&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel | CC-MAIN-2016-44 | refinedweb | 676 | 77.43 |
This is the mail archive of the gcc-patches@gcc.gnu.org mailing list for the GCC project.
Hi, I have attached an updated patch that addresses all the comments raised. On Fri, Apr 12, 2013 at 1:58 AM, Jakub Jelinek <jakub@redhat.com> wrote: > On Thu, Apr 11, 2013 at 12:05:41PM -0700, Sriraman Tallam wrote: >> I have attached a patch that fixes this. I have added an option >> "-mgenerate-builtins" that will do two things. It will define a macro >> "__ALL_ISA__" which will expose the *intrin.h functions. It will also >> expose all the target specific builtins. -mgenerate-builtins will not >> affect code generation. > > 1) this shouldn't be an option, either it can be made to work reliably, > then it should be done always, or it can't, then it shouldn't be done Ok, it is on by default now. There is a way to turn it off, with -mno-generate-builtins. > 2) have you verified that if you always generate all builtins, that the > builtins not supported by the ISA selected from the command line are > created with the right vector modes? This issue does not arise. When the target builtin is expanded, it is checked if the ISA support is there, either via function specific target opts or global target opts. If not, an error is raised. Test case added for this, please see intrinsic_4.c in patch. > 3) the *intrin.h headers in the case where the guarding macro isn't defined > should be surrounded by something like > #ifndef __FMA4__ > #pragma GCC push options > #pragma GCC target("fma4") > #endif > ... > #ifndef __FMA4__ > #pragma GCC pop options > #endif > so that everything that is in the headers is compiled with the ISA > in question I do not think this should be done because it will break the inlining ability of the header function and cause issues if the caller does not specify the required ISA. The fact that the header functions are marked extern __inline, with gnu_inline guarantees that a body will not be generated and they will be inlined. If the caller does not have the required ISA, appropriate errors will be raised. Test cases added, see intrinsics_1.c, intrinsics_2.c > 4) what happens if you use the various vector types typedefed in the > *intrin.h headers in code that doesn't support those ISAs? As TYPE_MODE > for VECTOR_TYPE is a function call, perhaps it will just be handled as > generic BLKmode vectors, which is desirable I think I checked some tests here. With -mno-sse for instance, vector types are not permitted in function arguments and return values and gcc raises a warning/error in each case. With return values, gcc always gives an error if a SSE register is required in a return value. I even fixed this message to not do it for functions marked as extern inline, with "gnu_inline" keyword as a body for them will not be generated. > 5) what happens if you use a target builtin in a function not supporting > the corresponding ISA, do you get proper error explaining what you are > doing wrong? Yes, please sse intrinsic_4.c test in patch. > 6) what happens if you use some intrinsics in a function not supporting > the corresponding ISA? Dunno if the inliner chooses not to inline it > and error out because it is always_inline, or what exactly will happen > then Same deal here. The intrinsic function will, guaranteed, to be inlined into the caller which will be a corresponding builtin call. That builtin call will trigger an error if the ISA is not supported. Thanks Sri > > For all this you certainly need testcases. > > Jakub
Attachment:
mmintrin_patch.txt
Description: Text document | http://gcc.gnu.org/ml/gcc-patches/2013-04/msg00999.html | CC-MAIN-2015-48 | refinedweb | 614 | 73.17 |
Obviously, we know the answer. This blog is intended to allow me to have an easy place to point people when they ask me “so what’s wrong with Docker”?
[To clarify, I use Docker myself, and it is pretty neat. All the more reason missing features annoy me.]
Docker itself:
- User namespaces — slated to land in February 2016, so pretty close.
- Temporary adds/squashing — currently “closed” and suggests people use work-arounds.
- Dockerfile syntax is limited — this is related to the issue above, but there are a lot of missing features in Dockerfile (for example, a simple form of “reuse” other than chaining). No clear idea when it will be possible to actually implement the build in terms of an API, because there is no link to an issue or PR.
Tooling:
- Image size — Minimal versions of Debian, Ubuntu or CentOS are all unreasonably big. Alpine does a lot better. People really should move to Alpine. I am disappointed there is no competition on being a “minimal container-oriented distribution”.
- Build determinism — Currently, almost all Dockerfiles in the wild call out to the network to grab some files while building. This is really bad — it assumes networking, depends on servers being up and assumes files on servers never change. The alternative seems to be checking big files into one’s own repo.
- The first thing to do would be to have an easy way to disable networking while the container is being built.
- The next thing would be a “download and compare hash” operation in a build-prep step, so that all dependencies can be downloaded and verified, while the hashes would be checked into the source.
- Sadly, Alpine linux specifically makes it non-trivial to “just download the package” from outside of Alpine. | https://moshez.wordpress.com/ | CC-MAIN-2016-07 | refinedweb | 295 | 63.7 |
- 2 minutes to read
IMPORTANT
You need a license to the DevExpress Office File API or DevExpress Universal Subscription to use these examples in production code. Refer to the DevExpress Subscription page for pricing information.
This article describes how to get started with the unit conversion component for .NET Framework and .NET Core.
Create a .NET Framework Application
Start Microsoft Visual Studio and create a new Windows Forms App (.NET Framework) project.
Right-click the References node in the Solution Explorer and select Add Reference. In the invoked Reference Manager dialog, add a reference to the DevExpress.Docs.v20.2.dll assembly.
Drop a Button from the Toolbox onto the form.
Double click the button. Add the following code to the button's Click event handler.
using DevExpress.UnitConversion; //... // The height is 5'4". QuantityValue<Distance> height = (5.0).Feet() + (4.0).Inches(); string s = String.Format("The height is {0} ells or {1} meters.", height.ToElls().Value.ToString("g3"), height.ToMeters().Value.ToString("g3")); MessageBox.Show(s);
Run the project and click the button.
Create a .NET Core Application
Start Microsoft Visual Studio and create a new Console Application (.NET Core) project.
Install the DevExpress.Document.Processor NuGet package.
Paste the code below in the Main method of the Program.cs file (Main procedure of the Module1.vb file for Visual Basic).
Run the project. | https://docs.devexpress.com/OfficeFileAPI/15113/unit-conversion-api/getting-started | CC-MAIN-2021-17 | refinedweb | 226 | 54.69 |
Generation?
JSP touts as an advantage that it takes an existing .jsp page and compiles that into a Servlet for speed and efficiency reasons. What this means is that it first parses the .jsp page into the resulting mess below and then it uses javac or your favorite Java compiler (ie: Jikes) to compile that Servlet into a .class file which is then loaded by the Servlet Engine. Wow, just explaining all of that gave me a headache, how about you?
The point being that using JSP is now a multi step process. The authors of JSP have done a good job of hiding this process stuff behind the scenes in such a way that you do not even notice it. One simply edits the .jsp page in their favorite editor and then uses their browser to call the page via a URI which starts the process of transforming it into a .class file.
There are some fundamental issues that are being dealt with in the generated .jsp template. The first one is the class name. What happens is that the engine needs to produce a name that is unique in order to work around class loader issues that might crop up. Therefore, each and every time one modifies a .jsp page, a new file is created on disk in the temporary directory. Unfortunately, this directory ends up growing in size until someone decides to clean it up. The engine could probably do this for you, except then it might make the mistake of actually removing the wrong file.
The point being that this whole process of edit->transform->compile->load->run is really unnecessary and in particular, a bad design. On the other hand, Velocity will simply load templates, parse them a single time and then store an Abstract Syntax Tree (AST) representation of the template in memory which can then be re-used over and over again. The process is simply edit->parse->run. The benefit is that working with Velocity templates ends up being much faster and it also removes the requirement of having a javac compiler and temporary scratch directory hanging around. In Velocity, when the template changes, the existing cached template is simply replaced with a freshly parsed version.
Another advantage to Velocity's approach for templates is that the actual template data can be stored anywhere, including a database or remote URI. By using configurable template loaders, it is possible to create template loaders that can do anything that you want.
Even without Turbine, Velocity offers several ways to deal with errors. Where frameworks such as Struts and Turbine come handy is by providing ways of properly dealing with errors. However, due to the fact that Struts is based on top of JSP, it also inherits the same amount of problems associated with JSP. The next chapter will go into more details on that.
One final problem in the design shown below is that the JSP page only catches Exception's. What if the code within a JSP page throws another exception like OutOfMemoryError? The problem here is that OOME is based on Throwable, not Exception. Therefore, it is much more difficult to catch this exception with just a JSP page. Future versions of the JSP spec and implementations will improve on this.
This nice example provided by our friends at NASA, which sends multi-billion dollar equipment through the heavens, is a perfect example of why JSP needs better error handling.
Buffering is also another big issue as constantly writing to the output stream is not very efficient.
<%@ page buffer="12kb" %> <%@ page autoFlush="true" %>
These are examples of telling JSP to buffer the output 12kb and to autoFlush the page. Struts+JSP has implemented the MVC model by providing the View portion through JSP templates. What part of the MVC model do you think that those tags belong? You guessed it, not the part where they are being used.
Velocity's approach to dealing with this issue is by allowing the developer to pass a stream into the rendering engine. If there is an exception thrown, during rendering, then the exception can be caught and dealt with. Buffering is also handled by passing properly buffered stream to the parser. Again, if there is an error, then another stream can be easily substituted for the output.
Here is an example of the intermediate code generated by Tomcat 3.3m2:
package jsp; import javax.servlet.*; import javax.servlet.http.*; import javax.servlet.jsp.*; import javax.servlet.jsp.tagext.*; public class helloworld_1 extends org.apache.jasper.runtime.HttpJspBase { static { } public helloworld_1( ) { } private static boolean _jspx_inited = false; public final void _jspx_init() throws org.apache.jasper.JasperException { }(); out.write("<html>\r\n<head><title>Hello</title></head>\r\n<body>\r\n<h1>\r\n"); if (request.getParameter("name") == null) out.write("\r\n Hello World\r\n"); else out.write("\r\n Hello, "); request.getParameter("name"); out.write("\r\n</h1>\r\n</body></html>\r\n"); } catch (Exception ex) { if (out != null && out.getBufferSize() != 0) out.clearBuffer(); if (pageContext != null) pageContext.handlePageException(ex); } finally { if (out instanceof org.apache.jasper.runtime.JspWriterImpl) { ((org.apache.jasper.runtime.JspWriterImpl)out).flushBuffer(); } if (_jspxFactory != null) _jspxFactory.releasePageContext(pageContext); } } }
You make the decision.
YmtdSayingHello <- Previous | Next -> YmtdErrorHandling | https://wiki.apache.org/velocity/YmtdGeneration | CC-MAIN-2016-50 | refinedweb | 877 | 57.37 |
Lab Exercise 2: Turtle Graphics
The purpose of this lab time is to give you more practice with python and writing programs, an introduction to turtle graphics and practice with the concepts of variables, operators, and functions.
Tasks
- Connect to your network directory. In the Finder under the Go menu, select Go to server. Enter fileserver1 into the server name field and then click connect. a window should pop up with several volumes on it, select Personal. A finder window should then come up with a folder with your username on it. You can do whatever you want inside that folder, such as creating directories or putting files. It's just like working with a flash stick. Since you can access those files from any networked computer on campus, please use your network directory to store all of your work from now on.
- Create a new file in BBEdit, or whatever editor you wish. Save the file as square.py
- Download the turtleUtils.py module and save it in your working directory. We'll use the turtleStart() and turtleWait() functions defined in that module to create the turtle window and keep it open after drawing is done.
- Using turtle graphics, write code for a square that is 50 pixels on a side. Test it out.
- Create a new variable called dx at the top of your code. Give it the value 50. Now modify your forward() instructions to use the parameter for the square size instead of the hard-coded number. Test it out.
- Create a new variable called dy at the top of your code. Interleave the use of dx and dy when you draw the square so that dx parameterizes the horizontal sides of the square and dy the vertical. Test it out.
- Create a new variable called angle at the top of your code. Before you make the first forward() call left() with angle as its argument. Test it out.
- Create two new variables called x0 and y0 at the top of your code. Give them initial values of 0. Before the call to left() have the pen lift up, use the function goto(x, y) to send the turtle to the location given by x0 and y0. Then put the pen down using the down() function.
- Create three new variables, red, green, and blue. Set each variable to a value between 0.0 and 1.0, where 1.0 is the maximum brightness for that color channel. Before any of the square is drawn, set the color by using the color(red, green, blue) function.
- Call the fill() function with an argument of 1 just before you draw the square. Then call it again after the square is done drawing. What happens?
- Put the following line just before you define the first variable.
def square():
Then tab in the rest of the commands that draw the square. All of the python commands that are tabbed in after the def statement are inside the function. You can now use the function square() to draw a square. After the function, make a call to the function square() by calling it (but don't tab it in, or it will be inside the function.
- Unfortunately, the funciton square() with no parameters draws the same square over and ver again because the size, location, orientation, and color are all hard-coded inside the function. Start to parameterize the function by first adding the parameters x0 and y0 to the def statement. The remove the two lines where hard-coded values are assigned to them within the function. Now the function will use the values passed in from outside.
def square(x0, y0):
Now you can call the function square() with two arguments such as square(0, 0) and square(50, 50) and get squares at different locations.
- Add more parameters to the function so that none of the values are hard-coded inside the function. Then have your program draw many rectangles of differing parameter values.
- Try making a Mondrian style image.
Once you've finished the above exercise, get started on the next project. | http://cs.colby.edu/courses/S08/cs151/labs/lab02/ | CC-MAIN-2017-51 | refinedweb | 685 | 75.4 |
Walkthrough: Inheriting from a Windows Forms Control with Visual C#
With Visual C# 2005, you can create powerful custom controls through inheritance. Through inheritance you are able to create controls that retain all of the inherent functionality of standard Windows Forms controls but also incorporate custom functionality. In this walkthrough, you will create a simple inherited control called ValueButton. This button will inherit functionality from the standard Windows Forms Button control, and will expose a custom property called ButtonValue.
When you create a new project, you specify its name in order to set the root namespace, assembly name, and project name, and to ensure that the default component will be in the correct namespace.
To create the ValueButtonLib control library and the ValueButton control
On the File menu, point to New and then click Project to open the New Project dialog box.
Select the Windows Control Library project template from the list of Visual C# Projects, and type ValueButtonLib in the Name box.
The project name, ValueButtonLib, is also assigned to the root namespace by default. The root namespace is used to qualify the names of components in the assembly. For example, if two assemblies provide components named ValueButton, you can specify your ValueButton component using ValueButtonLib.ValueButton. For more information, see; } }
This code sets the methods by which the ButtonValue property is stored and retrieved. The get statement sets the value returned to the value that is stored in the private variable varValue, and the set statement sets the value of the private variable by use of the value keyword.
From the File menu, choose Save All to save the project.
Controls are not stand-alone projects; they must be hosted in a container. In order to test your control, you must provide a test project for it to run in. You must also make your control accessible to the test project by building (compiling) it. In this section, you will build your control and test it in a Windows Form.
To build your. | http://msdn.microsoft.com/en-us/library/5h0k2e6x%28en-us,VS.90%29.aspx | crawl-003 | refinedweb | 335 | 52.7 |
: Mogre Tutorial - Embedding Mogre in Windows.Forms
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Source of version: 7
(current)
Original version by [ Culver] Any problems you encounter while working with this tutorial should be posted to the [ Forums]. {maketoc} !!Prerequisites This tutorial assumes you have knowledge of C# programming and are able to setup and compile an Mogre application (if you have trouble setting up your application, see ((Mogre Basic Tutorial 0)) for a detailed setup walkthrough). It also assumes that you know the basics of Windows.Forms usage. Additionally, his tutorial directly builds on the previous tutorial, so you should work through that one before starting on this one. !!Introduction In this tutorial I will be walking you through how to embed Ogre in a Windows.Forms window. A word of caution, in previous tutorials we have put all of our code into a single file (wrapped in a single namespace). In this tutorial you will probably be working with multiple files. If you receive errors in your program the first thing you should check is to make sure that all namespaces match up. As you go through the tutorial you should be slowly adding code to your own project and watching the results as we build it. !!Getting Started Unlike the previous tutorials, we will not be starting from a compilable code base. Be sure to follow these instructions carefully and make sure that at the end of this section you are able to run the program before continuing. !!!The Main Function Create a new Mogre project and clear out all of the contents of it. Create a new file (called program.cs) and add the following to it: {CODE(wrap="1", colors="c#")} using System; using System.Collections.Generic; using System.Windows.Forms; namespace Tutorial06 { static class Program { [STAThread] static void Main() { OgreForm form = new OgreForm(); form.Init(); form.Go(); } } } {CODE} !!!The Form In Visual Studios, right click on your project, click on Add, then "Windows Form...". Name the file "OgreForm.cs". Add two methods to this class, __Go__ and __Init__: {CODE(wrap="1", colors="c#")} public void Go() { } public void Init() { } {CODE} If you are using something other than Visual Studio to create this program, add a new class which derives from System.Windows.Forms.Form. We will not be using any Visual Studio's specific features in this tutorial, so you should not really have to do any translation. !!!Running the Application Make sure you can compile and run the application before continuing. If you are having difficulty, refer to the ((Mogre Basic Tutorial 0|project setup guide)) or post to [ forums]. Note that this program should do nothing until we add further code to it. If you run into problems which say something similar to: ''The type or namespace name 'OgreForm' could not be found (are you missing a using directive or an assembly reference?)'' then you probably have a namespace problem. Check to make sure that the "namespace" directive which wraps "program.cs" is the same as the one which wraps your form. !!The Init Function The ''Init'' function for our program will be very similar to the ''Init'' function in the previous tutorial. With the exception of the RenderWindow creation, we will not go into much detail about it since you should have already seen these concepts in the last tutorial. Before we add code to the ''Init'' function, we need to create an instance variable to hold the root object. At the beginning of the ''OgreForm'' class, add the following code: {CODE(wrap="1", colors="c#")} Root mRoot; RenderWindow mWindow; {CODE} Now we can add the following code to the ''Init'' function in the ''OgreForm'' class: {CODE(wrap="1", colors="c#")} // Create root object mRoot = new Root(); // Define Resources ConfigFile cf = new ConfigFile(); cf.Load("resources.cfg", "\t:=", true); ConfigFile.SectionIterator seci = cf.GetSectionIterator(); String secName, typeName, archName; while (seci.MoveNext()) { secName = seci.CurrentKey; ConfigFile.SettingsMultiMap settings = seci.Current; foreach (KeyValuePair<string, string> pair in settings) { typeName = pair.Key; archName = pair.Value; ResourceGroupManager.Singleton.AddResourceLocation(archName, typeName, secName); } } // Setup RenderSystem RenderSystem rs = mRoot.GetRenderSystemByName("Direct3D9 Rendering Subsystem"); // or use "OpenGL Rendering Subsystem" mRoot.RenderSystem = rs; rs.SetConfigOption("Full Screen", "No"); rs.SetConfigOption("Video Mode", "800 x 600 @ 32-bit colour"); // Create Render Window mRoot.Initialise(false, "Main Ogre Window"); NameValuePairList misc = new NameValuePairList(); misc["externalWindowHandle"] = Handle.ToString(); mWindow = mRoot.CreateRenderWindow("Main RenderWindow", 800, 600, false, misc); // Init resources TextureManager.Singleton.DefaultNumMipmaps = 5; ResourceGroupManager.Singleton.InitialiseAllResourceGroups(); // Create a Simple Scene SceneManager mgr = mRoot.CreateSceneManager(SceneType.ST_GENERIC); Camera cam = mgr.CreateCamera("Camera"); cam.AutoAspectRatio = true; mWindow.AddViewport(cam); Entity ent = mgr.CreateEntity("ninja", "ninja.mesh"); mgr.RootSceneNode.CreateChildSceneNode().AttachObject(ent); cam.Position = new Vector3(0, 200, -400); cam.LookAt(ent.BoundingBox.Center); {CODE} There are two new things we have done since the last tutorial. The first change is in how the RenderWindow is created. Here is that section of code again: {CODE(wrap="1", colors="c#")} mRoot.Initialise(false, "Main Ogre Window"); NameValuePairList misc = new NameValuePairList(); misc["externalWindowHandle"] = Handle.ToString(); RenderWindow window = mRoot.CreateRenderWindow("Main RenderWindow", 800, 600, false, misc); {CODE} To embed Ogre into a window which you create (as opposed to letting Ogre create its own window), you have to create a render window manually with Root's CreateRenderWindow function. We supply the Form's Handle to Ogre in the NameValuePairList parameter so that Ogre knows what window to render inside of. You can create multiple render windows this way, and you don't have to use a Form to render Ogre inside of. You may also use other types of controls (such as UserControl) to host Ogre. The second thing we have changed is we set the AutoAspectRatio of the Camera function: {CODE(wrap="1", colors="c#")} cam.AutoAspectRatio = true; {CODE} We will cover the reason for this change in the next section. !!The Constructor and Event Handlers There are two things we need to do in the constructor of our class. The first is to set the size of our Form to be 800 x 600. The second is to register event handlers for the Disposed and Resize events. Find ''OgreForm''~np~'s~/np~ constructor and add the following code to the very end: {CODE(wrap="1", colors="c#")} this.Size = new Size(800, 600); Disposed += new EventHandler(OgreForm_Disposed); Resize += new EventHandler(OgreForm_Resize); {CODE} When the form closes, we need to make sure that we cleanup our Root object (and also ensure that the render loop is no longer running). To do this, we will call the Root Object's Dispose method and setting the variable to null: {CODE(wrap="1", colors="c#")} void OgreForm_Disposed(object sender, EventArgs e) { mRoot.Dispose(); mRoot = null; } {CODE} Whenever the form is resized, we need to inform the RenderWindow of the new size: {CODE(wrap="1", colors="c#")} void OgreForm_Resize(object sender, EventArgs e) { mWindow.WindowMovedOrResized(); } {CODE} Since we set the AutoAspectRatio property of our Camera to be true (see the previous section), every time the window is resized, the Camera will be automatically updated to avoid stretching of the scene. Had we left that property to be the default value (false), the scene would strech whenever the window is resized. In this tutorial, we have set the resolution Ogre renders at to be 800 x 600 with this call: {CODE(wrap="1", colors="c#")} rs.SetConfigOption("Video Mode", "800 x 600 @ 32-bit colour"); {CODE} In practice, you should probably set the RenderSystem's resolution to be the maximum you expect the user to resize the window to. This should stop the scene from becoming pixelated when the window size is larger than the resolution Ogre is rendering at. Either that, or do not allow the user to resize the window. !!The Go Function The last thing we need to do is have our render loop run. Our general plan for this function is to first show the form, then start the render loop (which consists of rendering a frame and then pumping the application's event queue). We want this loop to run while mRoot != null (remember that when the form is Disposed the mRoot variable is set to null), and while mRoot.RenderOneFrame returns true. When RenderOneFrame returns false, it means that a FrameListener object has returned false, requesting that the application shut down. Here is the code to do this: (Add it to your ''Go()'' method) {CODE(wrap="1", colors="c#")} Show(); while (mRoot != null && mRoot.RenderOneFrame()) Application.DoEvents(); {CODE} That's it. Run the application to see Ogre rendering inside of a Windows Form. !!Pitfalls There are a few pitfalls I have run into when embedding Ogre in Windows Forms. Hopefully this section will help you solve some of the issues you may run into. !!!GDI and Transparency You may place Windows.Forms controls on top of the form/control which contains Ogre. However, you cannot make those controls transparent. Doing so will produce a noticable flicker in the rendering. I have never been able to find a way around this flicker which didn't involve manually filling a backbuffer. If anyone finds a way to get around this, I'd love to hear about it. !!!Constructors and the Forms Designer If you subclass Form, UserControl, or some other control to house Ogre, you must be careful not to put anything in the Constructor which requires Ogre to already be set up. If you do so, this will cause Visual Studio's forms designer to not work. For example, the following code would cause the forms designer to stop working if you put it in the constructor of your class: {CODE(wrap="1", colors="c#")} Root root = Root.Singleton; NameValuePairList misc = new NameValuePairList(); misc["externalWindowHandle"] = Handle.ToString(); mRoot.CreateRenderWindow("Main RenderWindow", 800, 600, false, misc); {CODE} On the other hand, this would work fine: {CODE(wrap="1", colors="c#")} Root root = Root.Singleton; if (root != null) { NameValuePairList misc = new NameValuePairList(); misc["externalWindowHandle"] = Handle.ToString(); mRoot.CreateRenderWindow("Main RenderWindow", 800, 600, false, misc); } {CODE} The second chunk of code works because it does not assume that Ogre has been set up already. In practice, this will probably be a subtler bug than the code above suggests. If you create a form or control which uses Ogre (directly or indirectly) and Visual Studio's Forms Designer refuses to load it, you should try the following things: # Clean the project, close Visual Studios, open Visual Studios, rebuild the project. # Make sure the Ogre DLLs are in your PATH statement (see ((Mogre Basic Tutorial 0|this)) for more information]]). # Make sure the form/control does not directly (or indirectly) use Ogre in its constructor (or in the constructors of any instance variables you have created). !!Source Code You can see the final state of this tutorial here: ((Mogre Tutorial - Embedding Mogre in Windows.Forms - Source)) You can also see a more fleshed out version of Ogre embedded in a form in the [ source code]. --- Alias: (alias(Mogre_Basic_Tutorial_6)) Alias: (alias(Mogre Basic
70 online users | https://wiki.ogre3d.org/tiki-pagehistory.php?page=Mogre+Tutorial+-+Embedding+Mogre+in+Windows.Forms&source=0 | CC-MAIN-2021-25 | refinedweb | 1,828 | 55.95 |
In this blog you will find attached a very simple usage of .NET interoperability with Dynamics NAV 2009 R2 with the objective of basic file management (move, copy, open, delete) WITHOUT using the FILE virtual table and is intended just to familiarize with this brand new feature proposed with NAV 2009 R2 release.
File management is made at client side (RoleTailored client side).
If you want to know more about .NET interoperability for NAV 2009 R2, please refer to MSDN link:
Extending Microsoft Dynamics NAV Using Microsoft .NET Framework Interoperability
.NET interoperability (variables) are generally based on the System.IO namespace:
System.IO.File
System.IO.Directory
System.IO.FileInfo
My ingredients:
- Microsoft Dynamics NAV 2009 R2
- Windows 7 Enterprise
What you will find in the TXT file:
- 2 Tables
- T.50100 Client Files Management Buffer
- T.50300 Client Files Management Setup
- 1 Page
- P.50200 Client Files Management
What to do to let it work (initial setup):
1. Populate the Client Files Management Setup table 50300 with the appropriate values :
- User ID -> windows login (without domain)
- Default From Path -> Initial path where to take the file from (NOTE: do not add the backslash at the end, the application will do this for you)
- Default To Path -> Path where to copy/move files to (NOTE: do not add the backslash at the end, the application will do this for you)
2. Once you have completed setup as per point 1, now you are really ready to manage files using the RTC and simply run Page 50200 Client Files Management.
Action buttons Legend:
Move Back - Move Forward
These are enabled since the beginning and permit the user to browse up and down the Directories hierarchy.
OPEN File - DELETE File
Once you have selected your source file (From File), these buttons will be shown. They permit the user to Open (a simple HYPERLINK) or delete the file selected. If the To file is selected (the "Done" option in the To File is selected) these actions refer to the To File. (Obviously you can change this how you wish, since you have the code under your fingers).
COPY File - MOVE File
These are the clue actions. They are enabled once the user has selected both the source file (From File) and the destination file (To File) and checked the 2 "Done" Options for "Manage File" and "Into File" groups (as reported in the first screenshot).
These postings are provided "AS IS" with no warranties and confer no rights. You assume all risk for your use.
Best Regards,
Duilio Tacconi (dtacconi)
Microsoft Dynamics Italy
Microsoft Customer Service and Support (CSS) EMEA
This is great page thanks.
It was very helpful to find out how can I copy an manage files in navsion.
So now I can easy copy file into my share point. I'll adapt some parts
to the link system in navision.
Thank Matthias | https://blogs.msdn.microsoft.com/nav/2011/01/12/manage-files-in-rtc-without-using-file-virtual-table-with-net-interop-and-nav-2009-r2/ | CC-MAIN-2018-05 | refinedweb | 482 | 62.27 |
01-06-2010 02:12 PM
Hello everyone. I have been working with the new OpenGL API for a few weeks now and I have some findings I would like to share and maybe a few people could comment on them. So far everything is working out well but we really need VBO.
1) Converting from floating point to fixed point for all my buffers (vertices, normals and texture coords) is actually slower. This was surprising and leads me to believe that the GPU uses full floats, which is pretty surprising. I can only speculate that the fixed point stuff is around for dynamic geometry that is being generated in fixed point for cpu performance reasons. Having the driver doing the conversion from fixed to float would be faster in native code. Comments?
2) FloatBuffers are terrible for dynamic geometry. It's actually faster to have a mirrored version in arrays for working and then put them in the FloatBuffer when done. This again was surprising. Maybe someone could comment on this?
3) This one is a shocker. My frame rate drops 20% when all my geometry is offscreen. I am not using view frustum culling since I felt the more I could put on the GPU the better. I am already carrying Java on my back
Perhaps RIM could supply a native function to do a basic sphere fustum check.
4) GLUtils.gluLookAt allocates memory. Thanks for the helper but I will be writting my own thank you.
5) Bitmap.scaleInto will destroy your alpha if you intend to make mipmaps on the fly. Hopefully this will save someone an hour or two.. Oddly enough the simulator supports auto mipmaps but the device doesn't.
6) It would be helpful to have a small doc talking about how the windowing is being done. Particularly I am interested in how the Bitmap that is used to create the Graphics works. I am talking about the Graphics that is supplied to eglWaitNative. When I create a surface using eglCreateWindowSurface, is it double buffered? What happens to the FullScreen.paint and FullScreen.paintBackground? What is the Bitmap that was used to create the Graphics used for? Could we get a sample showing how to use native fields like ButtonField overtop of an OpenGL scene?
7) I am concerned eglWaitNative, eglWaitGL and eglSwapBuffers blocking. Usually a graphics driver has a push buffer (DMA buffer) of commands that get built and swapbuffers does a flush not a finish. This allows the thread to continue to do other things and not block Is this what is happening?
01-06-2010 04:30 PM
Good to hear your research.
I would like to ask you if you ever encountered something like this before:
(The message posted at 11-24-2009 08:58 PM).
01-06-2010 04:52 PM
1) All my data is in floating point since I wanted to just get things going. I have recently made a conditional compile that will convert the data to fixed point once at load time. I have a static scene that I use to test frame rate and I went from 17fps with floating point to 14fps for fixed. It's pretty shocking. I can see it not gaining me anything as perhaps the scene is fill bound or bottled somewhere else but actually loosing frame rate is shocking. My test must be wrong somewhere. I will double check it.
3) Just ported my c stuff over. We shall see how it works. I noticed Andriod has a culling funciton for spheres.
4) Not sue how much memory. I just had it running in JDE with break when any object is created and it kept hitting it. That was enough for me. Allocation == evil.
5) True enough but it cost me a few hours figuring out why my textures stopped working on device.
It would be good to get more info on this as testing on the simulator is useless and the turn around time on device is brutal. I also ended up writing my own profiling since the on device one isn't very good.
01-06-2010 07:49 PM
1. That is odd, I wonder if it is some code oddity (I know there are cases of an app not working it App A is in the background, the WebBrowser is open, etc. etc., odd bugs like that).
3. Android, from what I remeber reading, doesn't have a full standards complient namespace. It has most of it but they wrote some extra functions in there.
4. It might be temporary allocation, each app has the ability to create local variables. It doesn't mean that the memory will remain allocated.
5. That always stinks.
01-07-2010 09:09 AM
1. I believe the BlackBerry smartphone does actually use floating point for buffer data (vertices, texcoords, etc), which would explain your findings. I'm working on confirming this for sure.
2. There is currently a bit of overhead when updating direct nio buffers (not just float buffers). Using a small number of bulk puts instead of a large number of smaller/single puts should definitely perform better today.
3. This is an odity of the GPU driver. I suggest doing your own view frustum culling. Java is no reason to leave culling/clipping to the gpu. Culling out huge numbers of triangles using a very fast frustum-sphere or frustum-box test will be way faster than leaving it to the driver to reject.
4. I've sent this to our development team for further investigation.
5. This has to do with the BlackBerry smartphone simulator using your desktop driver, which differs from that on the device itself.
6. I don't have any samples or documentation to offer on this. But I have collected your feedback and will be sending it to our documentation team.
7. eglWaitNative and eglWaitGL will block only if the graphics context is drawn to before or after making these calls. eglSwapBuffers actually does block today. This may also change eventually, but today it can be assumed that eglSwapBuffers does an internal glFinish.
01-07-2010 12:12 PM
Thank to everyone for the great responses.
1) I did some more test and I think some of my numbers have been off. If I have a fully static scene, no moving of camera or anything, then my frame rate usually starts off as 14fps. This pretty much remains the same even if I leave it for a minute. When I run the app the second or third time it will settle at 17fps. Since the device has to reboot every time I update, I suspect the OS is still doing stuff. With that said, I am finding no difference between fixed point and floating. The other numbers are correct.
3) I see your point to some extent but I can pretty much guarantee no one does there own clipping these days unless it's a special case such as portals. I can see culling for sure but I can also see not culling for some cases. It's one thing to make a graphical demo that uses all the CPU but another when you have collision and AI involved. So you need to retain every bit of CPU possible and make sure the GPU is fully untillized.
4) I would fully expect the allocation to be temp but wouldn't it still give the gc a chance to run? That is what I am ultimately concerned about.
5) I can understand that but it does make it much harder to develop if the simulator doesn't show similar results. It forces me to test on device much more often to see if the results are the same. Really GL_GENERATE_MIPMAP isn't in the GL10 namespace, it's in GL11.
7) That really helps. Thank you. I will try and make a render thread and see if I can reclaim some cycles.
All and all I am extremely happy/grateful that RIM has supported OpenGL ES. Now all we need is some audio mixing and we are good to go!
01-07-2010 02:52 PM
1. The device might be caching some pre-set values causing it to be slow. At least it seems to speed up afterwards.
4. It would give the gc a chance to run but MSohm said he sent it to the dev team so it might not last. By the way how did you get a function/breakpoint to be called whenever memory is allocated?
5. Nothing's perfect, when RIM ports the simulators over to Java so they work on Mac/Linux this might go away.
7. That does help.
Try System.getProperty("supports.mixing") to see if your BlackBerry supports audio mixing (running more then one audio Player at the same time). Unfortunately CDMA devices don't support audio mixing, if they could get that implemented that would be great but until then I will need to make my own audio mixer.
01-07-2010 03:14 PM
I tried putting the swap into a thread and got no benefit but it could simply be my poor Java skills or that my updating of the simulation is very light right now so there are no gains at this point. Here is my code I used.
class SwapThread extends Thread { public boolean m_bKill = false; public boolean m_bSwapping = false; public synchronized void renderStart() { m_EGL.eglWaitNative( EGL10.EGL_CORE_NATIVE_ENGINE, m_OffGraphics ); } public synchronized void renderEnd() { while( m_bSwapping == true ) { try { wait(); } catch( InterruptedException e ) { } } m_bSwapping = true; notifyAll(); } public void run() { while( m_bKill == false ) { synchronized( this ) { while( m_bSwapping == false ) { try { wait(); } catch( InterruptedException e ) { } } m_bSwapping = ); m_bSwapping = false; notifyAll(); } } } } private SwapThread m_SwapThread = new SwapThread(); //------------------------------------------------
---------------------------------------------- }
I looked at the support mixing property and its false for Storm and Storm 2. I also queried some of the JSR 234 properties and it looks like it's only camera stuff. It's funny you mention writing a mixer as I mentioned this before on the list. Now that my java is better I was going to try it again. Have you had any success? I just don't know if the cpu can handle all of this. Sorry for hating on java , but when arrays have bounds checking it really kills this sort of thing.
01-07-2010 03:38 PM
You have every right to hate on Java, it wasn't until recently that they actually tried speeding it up. Before that it was usually very slow unless you had a high-end computer. The good thing with BlackBerry is that the Java bytecode is converted to lower level code (from what I remember reading somewhere RAPC doesn't just copy the bytecode, it converts it to a lower level code type that reduces the amount of overhead of converting bytecode to the CPU's native ASM.).
The property, as you and I stated, returns false. If you search the forum you will find that this occurs only on CDMA devices, no idea why but I am not the one making cell phones.
I haven't even tried writing one. The thing is I like to go above and beyond so it may be nice to run two Players at the same time or to mix two audio streams together but I would want something that is limited only by the device it is running on, if I have the ability to mix 100 audio tracks together, I want to be able to. That is why I haven't written one yet but I plan to eventually. | http://supportforums.blackberry.com/t5/Java-Development/OpenGL-inital-findings/m-p/412700#M81612 | crawl-003 | refinedweb | 1,936 | 72.76 |
The Trouble with Constructors
December 14, 2010 — code, language, magpie
Every fledgling programming language exists somewhere on the continuum between “scratchings in a notebook” and “making Java nervous”. Right now, Magpie is farther to the right than total vaporware, but it’s not yet at the point where I actually want people to use it (though you’re certainly welcome to try). The big reason for that is that there’s some core pieces I’m still figuring out. Without those in place, any attempts to use the language will either fail or just be invalidated when I change something.
The biggest piece of that is the object system: how classes work. The two challenging parts of that are inheritance and constructors. I think I’ve got a few ideas that are finally starting to stick there, so I thought I’d start documenting them to make sure I’ve got it clear in my head, and hopefully get some feedback.
In this post, I’ll just worry about constructors. The way Magpie handles constructing instances of classes is a bit… uh… odd. I’ll explain Memento-style, starting with the end and working backwards to see how I got there. By the end (or is it the beginning?) it should hopefully make sense.
Making an Object
To see where we end up, here’s a simple class in Magpie:
class Point var x Int var y Int end
Pretty basic. It has two fields. Because those fields don’t have initializers
(i.e. they aren’t like
var z = 123), they need to get those values passed
in. Given that class up there, you can do that and make an instance like this:
var point = Point new(x: 1 y: 2)
That doesn’t look very special. So
new is just a static method on a class,
and you pass in named arguments? That’s half right.
new is just a static
(“shared” in Magpie-ese) method. Magpie doesn’t have named arguments. What it
has are records. The above is identical to:
var coords = x: 1 y: 2 var point = Point new(coords)
Records in Magpie are as they are in ML: structurally-typed anonymous
structs. A series of
keyword: value pairs forms a single expression that
evaluates to a record value. Sort of like object literals in Javascript,
although they’re statically-typed in Magpie.
So, this is pretty straightforward. When you define a class, it automatically
gets a shared method called
new that expects a record with fields that match
all of the required fields of the class?
Well, sort of. Actually,
new doesn’t do much at all. It’s just:
def new(arg) construct(arg)
OK, so what’s
construct?
Raw Constructors
Raw constructors are the real way that instances of a named class are created
in Magpie. Each class automatically gets a shared
construct method. That
method (like
new) takes a record with fields for all of the fields of the
class. It then builds an instance of the class and copies those field values
over.
So raw constructors are the real way that instances of a class are created in
Magpie. So what is
new for then?
A Time To Initialize
Calling
construct is the raw way to create an instance, but many (most?)
classes need to perform some initialization when an instance is created, or
maybe they’ll calculate the values of some of the fields instead of just
taking them in as arguments.
new exists to give you a place to do that.
For example, lets say we actually wanted to create points using polar coordinates, even though it stores Cartesian. In that case, we could define it like:
class Point shared def new(theta Int, radius Int -> Point) var x = cos(theta) * radius var y = sin(theta) * radius construct(x: x y: y) end var x Int var y Int end
As you can see
new is basically a factory method. It does some calculation,
and then the very last thing it does is call
construct, the real way to
create an object, and returns the result. (Like Ruby, a function implicitly
returns the result of its last expression.)
The reason Magpie always gives you both
construct and
new is for
forward-compatibility.
new is the way you should generally be creating
instances, so it gives you a default one that forwards to
construct. If you
later realize you need to do more initialization than just a straight call to
construct, you can replace
new without having to change every place you’re
creating an object.
OK, But Why?
So that seems pretty strange. Why on Earth would I design things this way instead of just using normal constructors like most other languages?
Let’s imagine that Magpie did have normal constructors (which it did until a few days ago, actually). Let’s translate our Point class to use that:
class Point // 'this' here defines a constructor method this(x Int, y Int) this x = x this y = y end var x Int var y Int end
Pretty straightforward, and it works fine. Now let’s break it:
class Point this(x Int, y Int) this x = x end var x Int var y Int end
Here, we’re failing to initialize the
y field. What is its value? We can fix
that the way Java does with
final fields by statically checking for
definite assignment. Part of the type-checking process will be to walk
through the constructor function and make sure every declared field in the
class gets assigned to. This isn’t rocket science, and I went ahead and
implemented that in Magpie too.
So we’re good, right? Well, what about this:
class Point this(x Int, y Int) doSomethingWithAPoint(this) this x = x this y = y end var x Int var y Int end
In the constructor, we’re passing
this to another function. That function,
reasonably enough, expects the Point it receives to be fully initialized, but
at this point it isn’t. So that’s bad.
We can fix that by making the static analysis even more comprehensive. While
we check for definite assignment, we’ll also track and make sure that
this
isn’t used until all fields are definitely assigned.
Of course, you need to be able to use
this to actually assign the fields. So
we’ll need to special-case that. At this point, it starts to look like we’re
building some ad-hoc typestate system where the static “type” of
this
mutates as we walk through the body of the constructor and gets tagged with
all of the fields that have been assigned to it. Like:
this(x Int, y Int) // here 'this' is "Point with no fields assigned" this x = x // now it's "Point with x" this y = y // now it's "Point with x and y" and we're good end
This is doable, but it’s a bit of a chore to implement. Much worse is that it’s a real chore for any (purely hypothetical at this point) Magpie user to have to know. In order to understand the weird type-check errors you can get in a constructor, you’ll have to fully understand all of this flow analysis I just described.
I’m trying to keep Magpie as simple as I can, and this is definitely not it.
Why Don’t Other Languages Have This Problem?
Here is where we get to the real motivation that leads to all of this. Java and C# don’t have this issue with their constructors. It’s perfectly valid to do this in Java:
class Point { public Point(int x, int y) { doSomethingWithPoint(x, y); this.x = x; this.y = y; } private final int x; private final int y; }
It’s bad form, but it’s safe. The reason why is because Java has default
initialization. Before you ever assign to a field in Java, it still has a
well-defined value. Numbers are 0, booleans are false, and reference types are
null.
Whoops! That last one is a doozy. I hate having to check for
null at
runtime. One of the major motivations for designing Magpie was to have it
statically eliminate the need for those. If I say a variable is of type
Monkey, I want it to always be a monkey, not “possibly a monkey, but also
possibly this other magical missing monkey value”.
The problem then is that it isn’t always possible to create a value of some
arbitrary type ex nihilo. We can’t just default initialize a field of
Monkey by creating a new monkey from scratch. Maybe it needs arguments to be
constructed.
So default initialization has to go. Every field in an instance of a class
will need to be explicitly initialized before anyone can use that instance. In
other words, until its fully set-up,
this is verboten.
(C++ has its own solution for this, of course: constructor initialization lists. They solve this problem neatly, but at the expense of adding a non- trivial amount of complexity to the language.)
The most straight-forward solution I could come up with was this: create the
instance as a single atomic operation. To do this, we’ll need to pass in
all of the fields the instance needs, and it will return us a fully-
initialized ready-to-use object. That’s
construct.
What’s nice about this is that it’s dead-simple. There’s almost no special
support in Magpie for constructors. No syntax for defining them. No special
definite assignment for tracking that fields are initialized. Just a single
built-in
construct method auto-generated by the interpreter for each class,
and you’re good to go.
It’s not all rosy, though. Doing things this way can be kind of gross if your
class has a lot of fields to initialize. You end up having to build a big
record as the last expression in your
new method.
The other challenge is that circular immutable data structures aren’t really feasible. (Magpie doesn’t have immutable fields yet, but it will.) Haskell has it even worse than Magpie since everything is immutable and it’s actually surprisingly tricky to solve it.
What may be the biggest drawback, though, is that it’s unusual. Unfamiliarity is its own steep cost, especially in a fledgling language.
Rewind
So, going from cause to effect, it’s:
To get rid of null references, I had to get rid of default initialization.
To get rid of default initialization, I had to get rid of access to
thisbefore an object has been fully-constructed.
To do that, I turned construction into a single
constructmethod that takes all of the required state and returns a new instance all in one step.
Then, to get user-defined initialization back, I wrapped that in a
newmethod that you can swap out to do what you want.
The reasoning seemed pretty sound to me, but I’m always eager to hear what others think about it. | http://journal.stuffwithstuff.com/2010/12/14/the-trouble-with-constructors/ | CC-MAIN-2014-42 | refinedweb | 1,856 | 72.16 |
A ListView delegate item with two labels and an optional image. More...
SimpleRow is a simple row intended to be used for ListView::delegate.
It shows a large text, a small detailText and an image or icon.
When using a ListPage, the ListView::model property is automatically set to a Component that creates SimpleRow objects.
SimpleRow automatically extracts properties from the ListView::model data objects. The following properties can be used:
text: string for the displayed text.
detailText: string for the displayed detailText.
icon: IconType for the displayed iconSource.
image: url for the displayed imageSource.
active: bool, whether the row should be highlighted.
visible: bool, whether the row should be shown at all.
enabled: bool, whether the row should be enabled, and click events emitted.
This way, the ListView::model can be chosen wisely so SimpleRow's properties do not have to be changed manually. The following code taken from the widget showcase app shows how its done:
AppListView { delegate: SimpleRow {} model: [ { text: "Widget test", detailText: "Some of the widgets available in Felgo AppSDK", icon: IconType.tablet }, { text: "Shown are:", detailText: "ListPage, NavigationBar with different items, Switch", icon: IconType.question } ] }
The ListView model objects can be accessed via the item property. This way, additional functionality can be added, like changing the text based on other properties:
AppListView { //some model with objects containing firstName and lastName properties model: DataModel.users delegate: SimpleRow { text: item ? item.firstName + " " + item.lastName : "" //override default text binding } }
Note: item is taken from the model and can be null when initializing the row object, so the
item ? ... : "" checks are necessary. } } } } } }
Find more examples for frequently asked development questions and important concepts in the following guides:
Chooses whether the row should be highlighted.
By default, this is bound to
item.active.
Whether the image should automatically change its size to match the height of the SimpleRow.
True by default.
A maximum height for the auto-sizing can bes set with the imageMaxSize property.
An optional value that's displayed as badge within the simple row.
The appearance of badge can be styled with the style property or globally with Theme::listItem properties:
import Felgo 3.0 App { onInitTheme: { // Badge styling Theme.listItem.badgeFontSize = 12 Theme.listItem.badgeTextColor = "white" Theme.listItem.badgeBackgroundColor = "grey" Theme.listItem.badgeRadius = 4 } ListPage { model: 1 delegate: SimpleRow { text: "Text" badgeValue: "12" } } }
This property was introduced in Felgo 2.16.1.
The small detail text to display at the bottom in the row.
By default, this is bound to
item.detailText.
The Icon item used for displaying the iconSource.
The source for the Icon to display at the left in the row. If not set, no icon is shown. Only either iconSource or imageSource should be set at a time.
By default, this is bound to
item.icon.
The RoundedImage item used for displaying the imageSource.
Maximum width or height of the image, if autoSizeImage is set to true.
This property was introduced in Felgo 2.6.2.
The source for the AppImage to display at the left in the row. If not set, no image is shown. Only either iconSource or imageSource should be set at a time.
By default, this is bound to
item.image.
If an array is used as the ListView::model for this row, this property contains the current element. The item is used per default for properties in SimpleRow and can also be accessed externally. If the model is not represented as an array, the SimpleRow properties cannot be initialized automatically.
It can be any JS object. When using a ListModel, item is set to null.
The StyleSimpleRow configuration sets the colors and sizes to be used for the SimpleRow. The default style uses the standard configuration of the Theme::listItem property.
This property was introduced in Felgo 2.6.2.
The large header text to display at the top in the row.
By default, this is bound to
item.text.
Voted #1 for: | https://felgo.com/doc/felgo-simplerow/ | CC-MAIN-2019-47 | refinedweb | 655 | 60.41 |
FG:FredericGlorieux
<<TableOfContents: execution failed [Argument "maxdepth" must be an integer value, not "[3]"] (see also the log)>>
Configure your environment
TODO. Text Editor with Mozilla ?
Source example
First of all, you should see a little of how XML looks. So let's take a very short document
<article> <title>XSLT, in hope to be simple</title> <author> <firstname>James</firstname> <lastname>Clark</lastname> </author> <author>Kay, Michael</author> <abstract> Sorry, James Clark and Michael Kay to use your names for a so dummy example. Please, consider that as a tribute. </abstract> <section> <title>section 1</title> <para> I don't now the exact story of <concept>XSL</concept>, but the guys behind that are very clever. </para> </section> </article>
This doc is more expressive than HTML, especially as I can change the names of elements (Schema/DTD) to express more precisely what I want (<abstract/>, <author/>). This is a not so bad way to store my texts, because they are structured, and quite self documented. Now, how do we take advantage of this? XSLT, of course.
Root
This will be the root XSL document in which all snippets will now go.
<?xml version="1.0" encoding="UTF-8"?> <xsl:transform <xsl:output <!-- here put your templates --> </xsl:transform>
<?xml version="1.0" encoding="UTF-8"?> This is the first declaration that all XML documents should have. Note the encoding precision: UTF-8 is default for XML. Languages other than English may need a different encoding. For an XSLT, leave it as UTF-8: your XML editor should know it.
<xsl:transform
Root element with a namespace declaration (XML-spec). All elements beginning with xsl:* are mapped as the namespace-uri "". This is the only string identifying your tags as XSLT instructions to process. This means you can also say
<myprefix:transform
This could be useful when an XSLT should output another XSLT. However, for now let's keep it simple: it will be easier for copy/paste. (By the way, also keep the @version attribute).
<xsl:output
An xsl:transform is a common XML document, that will be processed. All xsl:* elements will now be instructions to transform from an input to an output. Input should be valid XML, output could be text, xml, html (with unclosed tags, character entities like ...). This is the reason for @method attribute. Note @encoding, one more time, use UTF-8 for XML usages, ISO-8859-1 could be useful if you have a strange browser display.
Pull
As I've put some nice tags in my XML document, it's probably best to use them. For example, I want to extract title||author||abstract of my articles to have a short version. So let's write my first template to pull what I need in the source to output it. The pull method is the more intuitive for developpers, but definetely no the more efficient for XSL. But we need to begin ?
match, select, XPath
<!-- this template supposed to be in a xsl:transform described upper test it fastly, but delete it to continue this page ---> <xsl:template <!-- here, we are at root of the xml input, before the first element --> <xsl:copy-of </xsl:template>
<xsl:template The XSLT engine is a kind of filter, processing an XML input, with the stylesheet instructions. Imagine a complex search/replace, except instead of working on flat text it's working on a tree of elements. At first, the engine searching for a template matches the root. That's what is provided here, in the @match, with the "/" value. Unix users will quickly understand this syntax. Now, the current node will be the root of the XML input (like after a "change directory").
In fact, this very complex template is doing: nothing. Output should be almost exactly the same as the input in XML terms, except the encoding or some other xsl:output effects.
It's also a fast way to debug XSL, to say "Where am I?", "What's in?". The instruction copy-of outputs the nodes selected by the expression in @select, here: ".". The dot expresses the current node. It's another important characteristic of expressions, called XPath syntax.
But don't forget what we really want. From the input given upper, imagine you want short output for metadata extracting, to put in your database, or your search engine. You handle some precise and simple type of fields and documents.
<record> <title>XSLT, in hope to be simple</title> <description> Sorry, James Clark and Michael Kay to use your names for a so dummy example. Please, consider that as a tribute. </description> <creator>Clark, James</creator> <creator>Kay, Michael</creator> </record>
Take notice that order is a bit different from the source (a real reason to use Pull method), some names are different, you want to normalize the creator field.
<xsl:template <record> <!-- xsl:copy-of, not a good xsl practice --> <xsl:copy-of <!-- Better here, open an element, and put the value (text only) --> <description> <xsl:value-of </description> <!-- Begin a push logic, see below a template to handle <author/> --> <xsl:apply-templates </record> </xsl:template>
Now, I'm matching XML input with an <article/> root element (happily, it's my input). This will change the current node inside the template for all new XPath expressions (ex: @select). Note also the <record/> element, which is not in the XSLT namespace (no xsl: prefix), so the engine will interpret it as output. And now point the three ways to get content from source.
xsl:copy-of, working in the article context, so the @select is catching and ouputting the <title/> node.
xsl:value-of, same context as the copy-of but output only text.
xsl:apply-templates, here we are in more tricky, where XSLT power is. This mean, let the hand to some one who will handle specifically <author/> element.
Push
Push method means, process source document as it is, handle nodes by specific templates, and in context, stop, continue, or modify what you want. The most beautiful (and not so easy to understand) push stylesheet is the identity transformation. Instead of a big copy-of all input, imagine to process all nodes by default, and copy each one by one. Seems not very efficient, OK, but very powerful, let's see. Add this template to
The identity transformation. Simple and tricky, like nice computing concepts. It match and process all node() (<element/>, but also text(), <!- - comment() - ->...) and | attributes @* (see xsl:copy, xpath short
<xsl:template <!-- each node, copy it, only him, not his children --> <xsl:copy> <!-- process all children, handle by this template, or others :o) --> <xsl:apply-templates </xsl:copy> </xsl:template>
This a good start to now see how is processed your document. This will output all the node from source, so you will be able to verify if your stylesheet is handling what you want, like you want. At this step, if you have the match="article" and the match="@*|node()" templates, your output should be :
<record> <title>XSLT, in hope to be simple</title> <description> Sorry, James Clark and Michael Kay to use your names for a so dummy example. Please, consider that as a tribute. </description> <author> <firstname>James</firstname> <lastname>Clark</lastname> </author> <author>Kay, Michael</author> <author> <firstname>Dummy</firstname> </author> </record>
Indentation of your output depend on your xsl engine, but you see that the <article/> from the source is handle to write a <record/>, <title/> and <description/> are correctly handled, and the effect {{{<xsl:apply-templates }}} is now, copy each with children, like it is in the source. It means that the generic copy template has less priority than more precise matching match="article". This is a good way to begin to work and see what is going on. If you add this, all <author> (even where they are) will be rename to <creator>.
<xsl:template <creator> <xsl:apply-templates/> </creator> </xsl:template>
Remember, we don't to output <firstname/> and <lastname/> elements, but they are nice way to normalize name strings. So try to add these templates. They are not the most efficient in the world, but could give idea of how powerful could be to deal with priority of templates (implicit tests).
<!-- other processes could be added here one day ---> <xsl:template <xsl:value-of </xsl:template> <!-- in case of author witn lastname *and* fistname, we can reorder and add a comma --> <xsl:template <creator> <xsl:value-of <xsl:text>, </xsl:text> <xsl:value-of </creator> </xsl:template>
HTML
TODO
References
XSL in Docbook let masters talk
See Also
CHANGES
- 2004-07-16:FG more and refactoring
- 2003:FG creation
TODO
- an HTML section
- an easy and tested config for first step in XSL
- correct mistakes | https://wiki.apache.org/cocoon/BeginnerSimpleXSLT | CC-MAIN-2017-09 | refinedweb | 1,456 | 63.9 |
The objective of this post is to illustrate how to chain two SN74HC595 ICs and controlling them, using SPI, with the ESP8266.
Introduction
The objective of this post is to illustrate how to chain two SN74HC595 ICs and controlling them, using SPI, with the ESP8266. Naturally, the working principle is the same for using the shiftOut function instead of the SPI interface.
Working principle
The working principle of this method consists basically in putting the two shift registers of each IC in sequence.
As we seen in the previous post, when we transfer the serial data and a shift occurs, the last bit is discarded.But, if we use this last bit as the input of the shifting process of the second shift register, then this bit will not be lost and will be stored there. This process is illustrated in figure 1.
Figure 1 – Propagation of 1 bit between two chained SN74HC595.
So, if we start with a 8 bit sequence in the first IC and no values set in the second and then we transfer a new 8 bit block to the first, the previous sequence will be pushed, bit by bit, to the second IC, as can be seen in figure 2.
Figure 1 – Propagation of 8 bits between two chained SN74HC595.
Naturally, if we want to define the 16 bits (8 per IC) in one operation, we just send them uninterruptedly from the microcontroller and only in the end we send the load signal to both ICs. This way, the internal operation to transfer the bits from the shift registers to the storage registers will occur in parallel.
This approach scales if we want to add more ICs to extend the number of bits. For the generic case where we have N shift registers, we send N*8 bits uninterruptedly and, in the end, we send the load signal for each IC, in parallel. As before, the first byte that is transferred ends in the last IC of the chain and the last byte in the first IC.
Hardware
Figure 3 shows the connection diagram for chaining 2 SN74HC595 ICs and controlling them with the ESP8266.
Figure 3 – Diagram for chaining two SN74HC595 ICs.
As can be seen, we use exactly the same number of pins from the microcontroller we used before for controlling just one SN74HC595. So, we also connect the RCLK and SRCLK pins of the second IC to the Slave Select and clock pins of the ESP8266.
The only exception is that now we connect the QH’ of the first IC to the SER (corresponding to the Serial data input) pin of the second IC. If we remember what was explained in this previous post, the QH’ outputs the bit of the shift register that is discarded when the shift procedure occurs, when we are transferring the serial data.
So, like was explained in the previous section, if we transfer 16 bits instead of just 8, the first 8 bits will get propagated to the second IC.
Naturally, this design can be extended to include more SN74HC595 ICs, controllable with just 3 pins of the microcontroller. Nevertheless, we need to take in consideration that as we add more ICs to the chain, some propagation problems may occur, mainly related to noise. Also, since we would use 2 of the pins to control all of the ICs, the fan-out would need to be considered. Check this interesting discussion about the effects of chaining 40 of these devices.
Setup
The setup will be exactly the same as in the previous post and will allow the initialization of the SPI bus and of the Slave Select pin.
#include <SPI.h> const int SSpin = 15; void setup() { pinMode(SSpin, OUTPUT); SPI.begin(); }
Main loop
The code for the main loop of this tutorial is basically the same as the previous one, with just an extra line of code to transfer the second block of 8 bits. The code is shown below.
byte firstByte = 1; byte secondByte = 2; SPI.transfer(firstByte); SPI.transfer(secondByte);
Just remember that the first 8 bits (variable firstByte) will end in the second IC and the second 8 bits (variable secondByte) will stay in the first IC.
If we had more ICs chained, we would just need to add more SPI.transfer calls.
A slightly more interesting main loop function is shown bellow. In this case, we will do a for loop to set all the possible combinations of LEDs on/off for both ICs in parallel. So, the same sequence will occur in both.
void loop() { for (int i= 0; i<=7; i++){ digitalWrite(SSpin, LOW); //Disable any internal transference in the SN74HC595 SPI.transfer(i); //Transfer first byte SPI.transfer(i); //Transfer second byte digitalWrite(SSpin, HIGH); //Start the internal data transference in the SN74HC595 delay(3000); //Wait for next iteration } }
You can check the final result in the video below.
Just note that if we use the same code of the previous post, which corresponds to commenting one of the SPI.transfer methods, the second IC would show the same sequence of the first with a lag of one iteration. The video bellow shows this case.
Final notes
The possibility of extending the number of controlled bits (and thus output pins) by simply chaining these ICs offers great flexibility and helps solving many constraints when pins of a microcontroller are limited.
On top of that, the possibility of using SPI allows for using the same clock and MOSI pins for controlling other SPI devices (naturally, more Slave Select pins are needed).
One interesting combination consists on using this approach to control a led matrix, allowing for controlling an huge number of LEDs with a minimal number of pins of a microcontroller.
Related Posts
Resources
- Datasheet from Texas Instruments
- SPI library implementation for the ESP8266
- Discussion about chaining 40 74HC595
Technical details
- ESP8266 libraries: v2.3.0.
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This question already has an answer here:
When i run this code the output is "String"; if I hide the method that accepts a String parameter and run the code again then the output is "Object", so can anyone please explain me how this code works?
public class Example { static void method(Object obj) { System.out.println("Object"); } static void method(String str) { System.out.println("String"); } public static void main(String args[]) { method(null); } }
Compiler will choose most specific method, in this case, String is a sub class of Object, so the method with String as argument will be invoked.
From JLS 15.12.2.5.
Similar Questions | http://ebanshi.cc/questions/863191/passing-null-reference-in-a-method-parameter-in-java | CC-MAIN-2017-43 | refinedweb | 109 | 60.45 |
Hi all, I am wondering if anyone can help me as I havent been programming in c++ for a long time and just went back. I did some basic c++ before but kind of lost the touch.
The problem I am trying to do is return the values of an array of characters. See examples:
main.cpp
Code:#include <cstdlib> #include <iostream> #include "PPlayer.h" using namespace std; int main(int argc, char *argv[]) { system("cls"); PPlayer p; p.addFN("hoang"); cout<<p.retFN(); system("PAUSE"); //<- console pause to see result before exiting return EXIT_SUCCESS; };
PPlayer.h
Code:class PPlayer { char fname[30]; char lname[50]; int age; public: char* retFN(); void addFN(char[]); };
PPlayer.cpp
Code:#include <iostream> #include "PPlayer.h" char* PPlayer::retFN() { return fname; } void PPlayer::addFN(char fn[]) { strcpy(fname,fn); age = 1; return; }
It's pretty basic, as I am trying to do some test.
char * is a pointer and returning char* will return the address of the fname instead of the value in the array (I think that's what it does, cant remember my c++ much).
What i m wondering is, are there any other way of returning say the name enter : hoang
? | https://cboard.cprogramming.com/cplusplus-programming/67958-returning-arrays.html | CC-MAIN-2017-51 | refinedweb | 200 | 73.58 |
Learn what to expect in the new updates
Customizing plots with style sheets
Enter search terms or a module, class or function name.
All figure windows come with a navigation toolbar, which can be used to navigate through the data set. Here is a description of each of the buttons at the bottom of the toolbar
This button has two modes: pan and zoom. Click the toolbar button to activate panning and zooming, then put your mouse somewhere over an axes. Press the left mouse button and hold it to pan the figure, dragging it to a new position. When you release it, the data under the point where you pressed will be moved to the point where you released. If you press ‘x’ or ‘y’ while panning the motion will be constrained to the x or y axis, respectively. Press the right mouse button to zoom, dragging it to a new position. The x axis will be zoomed in proportionate to the rightward movement and zoomed out proportionate to the leftward movement. Ditto for the y axis and up/down motions. The point under your mouse when you begin the zoom remains stationary, allowing you to zoom to an arbitrary point in the figure. You can use the modifier keys ‘x’, ‘y’ or ‘CONTROL’ to constrain the zoom to the x axis, the y axis, or aspect ratio preserve, respectively.
With polar plots, the pan and zoom functionality behaves differently. The radius axis labels can be dragged using the left mouse button. The radius scale can be zoomed in and out using the right mouse button.
The following table holds all the default keys, which can be overwritten by use of your matplotlibrc (#keymap.*).
If you are using matplotlib.pyplot the toolbar will be created automatically for every figure. If you are writing your own user interface code, you can add the toolbar as a widget. The exact syntax depends on your UI, but we have examples for every supported UI in the matplotlib/examples/user_interfaces directory. Here is some example code for GTK:
from matplotlib.figure import Figure from matplotlib.backends.backend_gtkagg import FigureCanvasGTKAgg as FigureCanvas from matplotlib.backends.backend_gtkagg import NavigationToolbar2GTKAgg as NavigationToolbar win = gtk.Window() win.connect("destroy", lambda x: gtk.main_quit()) win.set_default_size(400,300) win.set_title("Embedding in GTK") vbox = gtk.VBox() win.add(vbox) fig = Figure(figsize=(5,4), dpi=100) ax = fig.add_subplot(111) ax.plot([1,2,3]) canvas = FigureCanvas(fig) # a gtk.DrawingArea vbox.pack_start(canvas) toolbar = NavigationToolbar(canvas, win) vbox.pack_start(toolbar, False, False) win.show_all() gtk.main() | https://matplotlib.org/1.4.3/users/navigation_toolbar.html | CC-MAIN-2022-33 | refinedweb | 429 | 58.28 |
Red Hat Bugzilla – Bug 350101
Anaconda aligns partitions suboptimally for RAID disks
Last modified: 2009-05-04 06:01:57 EDT
Description of problem:
Anaconda tries to align partitions to legacy C/H/S geometry. This is nice for
dual-booting with other operating systems, but Linux doesn't care about C/H/S
geometry, while RAID arrays *do* care about alignment. Anaconda should at the
very least offer a non-default option to optimize partitions for RAID use. EMC
currently recommends that their customers do some expert-mode hacking with fdisk
to partition storage on their SANs, which is inconvenient and prone to error.
Version-Release number of selected component (if applicable):
all released versions
How reproducible:
100%, at least on platforms using MSDOS disklabels. Probably somewhat of an
issue on all platforms.
Steps to Reproduce:
1. Install RHEL
2. Run parted -s /dev/sda unit s print
Actual results:
Number Start End Size Type File system Flags
1 63s 208844s 208782s primary ext3 boot
2 208845s 312287534s 312078690s primary lvm
3 312287535s 312496379s 208845s primary ext3
Expected results:
Keeping the current behavior by default is okay, but an enterprise OS should
give the user a convenient option to align partitions for RAID storage, which
typically has 32768 or 65536 byte stripes.
Additional info:
It might also be nice to use this info to set the ext3 stripe size, when possible.
It would be quite intuitive if I could add '--align 64k' to a 'part' command in
a kickstart file and have it do the right thing.
Playing around with things a bit, it seems that fdisk and sfdisk strongly
encourage C/H/S geometry, while parted is quite happy with arbitrary resolution.
The big catch is that parted uses *inclusive* arithmetic, and arguably
incorrectly, for sizing the end of a partition. For example:
parted -s /dev/sda mkpart primary 1 2
Will create a partition whose first sector is at precisely 1 MiB and whose last
sector is at precisely 2 MiB. If you want to do it right, you need to set "unit
s" in parted and subtract 1 from the end address. For example:
parted -s /dev/sda unit s mkpart primary 128 204927
Will create a partition that is precisely 100 MiB in size, 64 KiB aligned, just
after the MBR and partition table, assuming 512 byte sectors.
It should be noted that some SANs present 2048 byte sectors to the OS, and 4096
byte sectors will soon be standard, so the sector size and precise sector count
should be read explicitly.
Since my python sucks, but I needed arbitrary precision integer math to handle
large volumes, I developed a shell front-end and python back-end to create
partitions of specified sizes (plus using the rest in a final partition, so
specifying no sizes uses the whole disk) with the specified alignment. I have
used these successfully in %pre on a test system. Please consider these
examples only. This was my first complete python script.
#!/bin/bash
# partalign.sh
# front-end to partalign.py
if [ $# -lt 2 ]; then
echo 'usage:'
echo 'partalign.sh device align_kiB [part1_MiB...]'
exit 1
fi
DEVICE=$1
dd if=/dev/zero of=$DEVICE bs=4k count=4k
parted -s $DEVICE mklabel msdos
SECTOR_B=$(parted -s $DEVICE unit B print | grep -F Sector | cut -d ' ' -f 4 |
cut -d B -f 1)
TOTAL_S=$(parted -s $DEVICE unit s print | grep -F Disk | cut -d ' ' -f 3 | cut
-d s -f 1)
python partalign.py $SECTOR_B $TOTAL_S "$@"
#!/usr/bin/python
# partalign.py
import os
import sys
def dopart(dev, part, start, end):
rc = os.spawnvp(os.P_WAIT, "parted", ("-s", dev, "unit", "s", "mkpart",
part, str(start), str(end)))
if rc != 0:
sys.exit(rc)
if len(sys.argv) < 5:
print("Not enough arguments")
sys.exit(1)
sector_b = long(sys.argv[1])
total_s = long(sys.argv[2])
device = sys.argv[3]
align_kb = long(sys.argv[4])
if align_kb <= 0:
print("Invalid alignment")
sys.exit(2)
elif align_kb > 1024:
print("Alignment too large")
sys.exit(3)
align_s = (align_kb * 1024) / sector_b
# truncate the slack, and remember that parted uses inclusive addressing
last_s = (total_s - (total_s % align_s)) - 1
# leave plenty of room for mbr, partition table, etc.
reserve_kb = 64
reserve_s = (reserve_kb * 1024) / sector_b
while reserve_s < align_s:
reserve_s *= 2
start_s = reserve_s
parttype = "primary"
count = 0
args = range(len(sys.argv))
for i in args:
if i < 5:
continue
count += 1
# do we need an extended partition?
if count == 4:
# use the full physical space, so the slack can be used later
dopart(device, "extended", start_s, total_s - 1)
count += 1
start_s += reserve_s
parttype = "logical"
continue
# linux only supports 15 partitions per disk
elif count == 15:
break
if sys.argv[i] <= 0:
break
part_mb = long(sys.argv[i])
part_s = (part_mb * 1024 * 1024) / sector_b
# end_s is inclusive
end_s = start_s + part_s - 1
if (end_s > last_s):
break
dopart(device, parttype, start_s, end_s)
start_s += part_s
# if there's any room left, use it
if start_s <= last_s:
dopart(device, parttype, start_s, last.
Does this problem remain true for Fedora 9?
Does this problem remain true for RHEL-5.3? | https://bugzilla.redhat.com/show_bug.cgi?id=350101 | CC-MAIN-2017-04 | refinedweb | 844 | 62.38 |
BBC micro:bit
IR Break Beam Sensor
Introduction
This IR Break Beam sensor comes in two parts as you can see in the image. It is sold by the US electronics company Adafruit and can be picked up from online suppliers in the UK.
On the right, you have an emitter that sends out infrared light. On the left, you have a receiver. When these are lined up, the receiver senses the IR light which can be read on the yellow signal line. The beam can be up to 50cm if using 5 volts, a bit less using the onboard 3V3 supply.
The sensor isn't cheap but it gives a quick, accurate reading that makes it usable in some interesting projects.
Circuit
Connect the ends as follows and line up the emitter and receiver to make your beam. Go for about 10cm for a test.
Program
Here's a simple test program to see if the sensor works. There is some serial output to help you know what is going on. Open up the REPL window or use a terminal emulator to see the printed output.
from microbit import * last_reading = 0 print("Beam Ready") while True: pin0.write_digital(1) reading = pin0.read_digital() if reading==0 and last_reading==1: display.show(Image.HAPPY) print("Broken at", running_time()) print("Pausing") sleep(1000) display.clear() print("Beam Ready") last_reading = reading sleep(20)
Challenges
- Buzzers and more lights would make for a decent burglar alarm or a more advanced version of the Feline Detection System.
- The break beam makes an interesting switch. You can trigger it with hands or feet.
- If you have a table top football game of some variety, you could add your own goal line technology system.
- Any miniature, table top game that has some sort of aiming and hitting component, like tiddlywinks or basketball.
- Make a suitable target and aim ping pong balls at it to score points.
- Make a reaction game. Display an image after a random amount of time. Use the break beam to determine how long it took the person to react.
- Using two of these sensor kits, you can do reasonably accurate timing and speed calculations. Cut out any lines of code that you don't need and reduce the gap between readings. Measure the distance between the sensors. Write a program to calculate the time difference between each of the sensors firing. With the distance and time, it is possible for you to work out the speed of whatever object was breaking the two beams. | http://www.multiwingspan.co.uk/micro.php?page=break | CC-MAIN-2019-09 | refinedweb | 421 | 74.79 |
Paul Rubin wrote: > def some_gen(): > ... > yield *some_other_gen() > > comes to mind. Less clutter, and avoids yet another temp variable > polluting the namespace. > > Thoughts? Well, not directly related to your question, but maybe these are some ideas that would help determine what we think generators are and what we would like them to become. I'm currently also fascinated by the new generator possibilities, for example sending back a value to the generator by making yield return a value. What I would like to use it for is when I have a very long generator and I need just a slice of the values. That would mean running through a loop, discarding all the values until the generator is in the desired state and only then start doing something with the output. Instead I would like to directly set or 'wind' -like a file- a generator into some specific state. That would mean having some convention for generators signaling their length (like xrange): >>> it = xrange(100) >>> len(it) 100 >>> Note: xrange didn't create a list, but it has a length! Also we would need some convention for a generator to signal that it can jump to a certain state without computing all previous values. That means the computations are independent and could for example be distributed across different processors or threads. >>> it = range(100) >>> it] >>> But currently this doesn't work for xrange: >>> it = xrange(100) >>> it[50:] Traceback (most recent call last): File "<stdin>", line 1, in ? TypeError: sequence index must be integer >>> Even though xrange *could* know somehow what its slice would look like. Another problem I have is with the itertools module: >>> itertools.islice(g(),10000000000000000) Traceback (most recent call last): File "<stdin>", line 1, in ? ValueError: Stop argument must be a non-negative integer or None. >>> I want islice and related functions to use long integers for indexing. But of course this only makes sense when there already are generator slices possible, else there would be no practical way to reach such big numbers by silently looping through the parts of the sequence until one reaches the point one is interested in. I also have thought about the thing you are proposing, there is itertools.chain of course but that only works when one can call it from 'outside' the generator. Suppose one wants to generate all unique permutations of something. One idea would be to sort the sequence and then start generating successors until one reaches the point the sequence is completely reversed. But what if one wants to start with the actual state the sequence is in? One could generate successors until one reaches the 'end' and then continue by generating successors from the 'beginning' until one reaches the original state. Note that by changing the cmp function this generator could also iterate in reverse from any point. There only would need to be a way to change the cmp function of a running generator instance. from operator import ge,le from itertools import chain def mutate(R,i,j): a,b,c,d,e = R[:i],R[i:i+1],R[i+1:j],R[j:j+1],R[j+1:] return a+d+(c+b+e)[::-1] def _pgen(L, cmpf = ge): R = L[:] yield R n = len(R) if n >= 2: while True: i,j = n-2,n-1 while cmpf(R[i],R[i+1]): i -= 1 if i == -1: return while cmpf(R[i],R[j]): j -= 1 R = mutate(R,i,j) yield R def perm(L): F = _pgen(L) B = _pgen(L,le) B.next() return chain(F,B) def test(): P = '12124' g = perm(P) for i,x in enumerate(g): print '%4i) %s' %(i, x) if __name__ == '__main__': test() A. | https://mail.python.org/pipermail/python-list/2007-April/430397.html | CC-MAIN-2020-05 | refinedweb | 624 | 59.84 |
How to get Control back of parent browser
By
MakzNov
- zuladab")
- By Seminko
Hey $sPicker = "color" Then If $data_ID_value = '????' Or $data_ID_value = "????" Then $oReturnList = $tag.GetElementsByTagName("a") EndIf ElseIf $sPicker = "network" Then If $data_ID_value = '????' Then $oReturnList = $tag.GetElementsByTagName("a") EndIf ElseIf $sPicker = "storage" Then If $data_ID_value = '????' Then $oReturnList = $tag.GetElementsByTagName("a") EndIf EndIf Next EndIf Return $oReturnList EndFunc $oColorList = GetObjectList("color") For $oColor In $oColorList If StringInStr($oColor.GetAttribute("aria-disabled"), "true") <= 0 Then ; remove object from the collection ??? EndIf Next
- By nooneclose
my FF.au3 does get included but my script does not open firefox.
here is my code so far:
#include <FF.au3> _FFStart("", Default, 0) I am using firefox portable version 52.0 Any and all help would be greatly appreciated.
The code runs but nothing happens. I think the FF.au3 cannot find or connect to the firefox portable.
- | https://www.autoitscript.com/forum/topic/194112-how-to-get-control-back-of-parent-browser/?tab=comments | CC-MAIN-2021-10 | refinedweb | 142 | 55 |
Retrieving a random Option from HTML DropDown using Grails Functional Testing
I have recently started using the marvelous plugin Grails function Testing by Marc Palmer ().I would like to share few things with you about this plugin.
The purpose of testing get defeated if we keep on doing for the same values. The method below let you to do it for the different values each time.
def countryList = byName(’country’)
int randomIndex=new Random().nextInt(
countryList.getOptionSize()
)
selects[’country’].select countryList.getOption(randomIndex).getValueAttribute()
byName() retrieve the element from the current page by its name attribute. Throws exception if multiple elements found with same name and null if no element found
In above example I am retrieving the select element of current page which has the name attribute ‘country’.
getOption() takes the integer as a parameter and return the option element of the current page at index 2
getValueAttribute() useful to get what the value need to be passed as params to the server. This method assures that value is passed rather than the name displyed in the list.
I hope this would help some of you.
Hope it helps
Uday Pratap Singh
uday@intelligrape.com
Hey….
nice blog….
took me out of a serious error i was doing… | http://www.tothenew.com/blog/retrieving-a-random-option-from-html-dropdown-using-grails-functional-testing/ | CC-MAIN-2019-39 | refinedweb | 209 | 54.73 |
Objectives
- Use the I2C bus with several devices.
- Connect several I2C devices to the same bus.
- Visualize on a LCD display the date and time read via an RTC.
BILL OF MATERIALS
INTRODUCTION AND ASSEMBLY
We have already used different I2C devices in several chapters, but so far we have always done it in isolation. And the good thing when using the I2C interface is that it allows us to connect and control several devices of this kind very easily. If you are not familiar with the I2C bus we recommend you, before going ahead, taking a look at the chapter in which is explained in enough detail what it is and how it works, using precisely the LCD display that we also use in this chapter. And in the same way, if the RTC doesn’t ring a bell here is the corresponding chapter.
If you have already these two subjects under control, you will see how to integrate the two components into a single assembly and within a single sketch is very easy. The only thing you have to bear in mind is which address is associated to each device, and define it correctly in the sketch. And in the case of this RTC, you do not even have to do that, since the own library manages it by itself.
As for the assembly, the two devices share the same Vcc and GND pins for the power supply, and of course the pins corresponding to the I2C bus: SCA and SCL, which in the case of the Arduino UNO correspond to the pins A4 and A5. As you can see, thanks to this bus we have saved a lot of wires and it makes it much easier to include new devices of this kind, just in case we want to expand our project.
PROGRAMMING
If the assembly did not have too much mystery, the sketch is just as simple. To begin, we will include the libraries we are going to use, define a variable with the address of the LCD (in the case of the RTC is not necessary) and create an instance of type LiquidCrystal_I2C:
#include <Time.h> #include <Wire.h> #include <DS1307RTC.h> // a basic DS1307 library that returns time as a time_t #include <LCD.h> #include <LiquidCrystal_I2C.h> #define I2C_ADDR 0x27 LiquidCrystal_I2C lcd(I2C_ADDR, 2, 1, 0, 4, 5, 6, 7);
Inside the setup function we initialize the LCD, indicating that it is a 16 × 2 LCD display, and setting the RTC to the correct date and time:
void setup() { Serial.begin(115200); lcd.begin (16, 2); // Initialize the display with 16 characters and 2 lines lcd.setBacklightPin(3, POSITIVE); lcd.setBacklight(HIGH); // while (!Serial) ; // Only for the Arduino Leonardo setSyncProvider(RTC.get); // We use the RTC setTime(10, 40, 00, 14, 11, 2016); // 14 November 2016, 10:40:00 if (timeStatus() != timeSet) Serial.println("Unable to sync with the RTC"); else Serial.println("RTC has set the system time"); }
And once it is done we will reuse the functions we use in the RTC chapter, but instead of showing it on the display we will use the LCD library to display the time and date on the LCD:
void digitalClockDisplay() { lcd.home (); // Go home lcd.print(hour()); printDigits(minute()); printDigits(second()); lcd.setCursor ( 0, 1 ); // Go to the 2nd line lcd.print(day()); lcd.print("/"); lcd.print(month()); lcd.print("/"); lcd.print(year()); } void printDigits(int digits) { lcd.print(":"); if (digits < 10) lcd.print('0'); lcd.print(digits); } void printDigits(int digits) { lcd.print(":"); if (digits < 10) lcd.print('0'); lcd.print(digits); }
And finally we have just to call this function every second to show the date and time:
void loop() { digitalClockDisplay(); delay(1000); }
You can download here the full sketch:Sketch 61.1
WHAT TO DO IF SEVERAL DEVICES HAVE THE SAME ADDRESS
At this point someone could have thought about connecting several devices of the same kind that have the same address. As almost everything, this has already happened to someone previously, and that is why I2C devices usually have a pair of connections labelled C1 and C2, so you can change the direction by welding or cutting these tracks, which allows up to 4 different addresses.
UOnce changed you just have to use the program I2C scanner and see which is its new address to assign it.
SUMMARY
In this chapter we have learnt several important things:
- We have learnt to connect several I2C devices.
- It is very easy to use several I2C devices in the same sketch.
- We know now how to change the address of these kind of devices.
Give a Reply | http://prometec.org/advanced-tools/combining-several-i2c-devices/ | CC-MAIN-2021-49 | refinedweb | 774 | 70.02 |
Nov 23, 2010 04:39 PM|hsamdani|LINK
I am currently working on a project to integrate WCF custom fault along with enterprise library exception block.
I was following Guy Burstein's blog for doing this :
This example only shows mapping for message and id. The message is of string data type and id is Guid data type.
But what if I have some other custom fields in my custom Fault object in which I have a CategoryID of type string to which I need to map the id of type Guid ?
When I try to do the mapping and propogate it, I get the value as null. Is there some way I could convert the Guid to string type while doing the mapping in EL?
[DataContract]<div style="FONT-SIZE: 10pt; BACKGROUND: white; COLOR: black; FONT-FAMILY: consolas" mce_style="FONT-SIZE: 10pt; BACKGROUND: white; COLOR: black; FONT-FAMILY: consolas">
public class ServiceFault
{
private string categoryCode;
private string message;
[DataMember][DataMember]
public string CategoryCode
{
get { return categoryCode; }
set { categoryCode = value; }
}
[DataMember]
public string MessageText
{
get { return message; }
set { message = value; }
}
}
</div></div>
0 replies
Last post Nov 23, 2010 04:39 PM by hsamdani | http://forums.asp.net/t/1626316.aspx?EL+Exception+Handling+block+and+WCF+custom+Service+Fault+Exception | CC-MAIN-2015-18 | refinedweb | 194 | 53.85 |
go-chartgo-chart
Package
chart is a very simple golang native charting library that supports timeseries and continuous line charts.
Master should now be on the v3.x codebase, which overhauls the api significantly. Per usual, see
examples for more information.
InstallationInstallation
To install
chart run the following:
> go get -u github.com/wcharczuk/go-chart
Most of the components are interchangeable so feel free to crib whatever you want.
Output ExamplesOutput Examples
Spark Lines:
Single axis:
Two axis:
Other Chart TypesOther Chart Types
Pie Chart:
The code for this chart can be found in
examples/pie_chart/main.go.
Stacked Bar:
The code for this chart can be found in
examples/stacked_bar/main.go.
Code ExamplesCode Examples
Actual chart configurations and examples can be found in the
./examples/ directory. They are simple CLI programs that write to
output.png (they are also updated with
go generate.
UsageUsage
Everything starts with the
chart.Chart object. The bare minimum to draw a chart would be the following:
import ( ... "bytes" ... "github.com/wcharczuk/go-chart" //exposes "chart" ) graph := chart.Chart{ Series: []chart.Series{ chart.ContinuousSeries{ XValues: []float64{1.0, 2.0, 3.0, 4.0}, YValues: []float64{1.0, 2.0, 3.0, 4.0}, }, }, } buffer := bytes.NewBuffer([]byte{}) err := graph.Render(chart.PNG, buffer)
Explanation of the above: A
chart can have many
Series, a
Series is a collection of things that need to be drawn according to the X range and the Y range(s).
Here, we have a single series with x range values as float64s, rendered to a PNG. Note; we can pass any type of
io.Writer into
Render(...), meaning that we can render the chart to a file or a resonse or anything else that implements
io.Writer.
API OverviewAPI Overview
Everything on the
chart.Chart object has defaults that can be overriden. Whenever a developer sets a property on the chart object, it is to be assumed that value will be used instead of the default.
The best way to see the api in action is to look at the examples in the
./_examples/ directory.
Design PhilosophyDesign Philosophy
I wanted to make a charting library that used only native golang, that could be stood up on a server (i.e. it had built in fonts).
The goal with the API itself is to have the "zero value be useful", and to require the user to not code more than they absolutely needed.
ContributionsContributions
Contributions are welcome though this library is in a holding pattern for the forseable future. | https://go.ctolib.com/go-chart.html | CC-MAIN-2019-51 | refinedweb | 422 | 59.4 |
Contents
- Lesson Goals
- Example 1: Fetching and Parsing HTML
- Example 2: URL Queries and Parsing JSON
- Example 3: Advanced APIs
Lesson Goals
OpenRefine is a powerful tool for exploring, cleaning, and transforming data. An earlier Programming Historian lesson, “Cleaning Data with OpenRefine”, introduced the basic functionality of Refine to efficiently discover and correct inconsistency in a data set. Building on those essential data wrangling skills, this lesson focuses on Refine’s ability to fetch URLs and parse web content. Examples introduce some of the advanced features to transform and enhance a data set including:
- fetch URLs using Refine
- construct URL queries to retrieve information from a simple web API
- parse HTML and JSON responses to extract relevant data
- use array functions to manipulate string values
- use Jython to extend Refine’s functionality
It will be helpful to have basic familiarity with OpenRefine, HTML, and programming concepts such as variables and loops to complete this lesson.
Why Use OpenRefine?
The ability to create data sets from unstructured documents available on the web opens possibilities for research using digitized primary materials, web archives, texts, and contemporary media streams. Programming Historian lessons introduce a number of methods to gather and interact with this content, from wget to Python. When working with text documents, Refine is particularly suited for this task, allowing users to fetch urls and directly process the results in an iterative, exploratory manner.
David Huynh, the creator of Freebase Gridworks (2009) which became GoogleRefine (2010) and then OpenRefine (2012+), describes Refine as:
- more powerful than a spreadsheet
- more interactive and visual than scripting
- more provisional / exploratory / experimental / playful than a database 1
Refine is a unique tool that combines the power of databases and scripting languages into an interactive and user friendly visual interface. Because of this flexibility it has been embraced by journalists, librarians, scientists, and others needing to wrangle data from diverse sources and formats into structured information.
OpenRefine terminal and GUI
OpenRefine is a free and open source Java application. The user interface is rendered by your web browser, but Refine is not a web application. No information is sent online and no internet connection is necessary. Full documentation is available on the official wiki. For installation and staring Refine check this workshop page.
Note: this lesson was written using openrefine-2.7. Although almost all functionality is interchangeable between versions, I suggest using the newest version.
Lesson Outline
This lesson presents three examples demonstrating workflows to harvest and process data from the web:
- Example 1: Fetching and Parsing HTML transforms an ebook into a structured data set by parsing the HTML and using string array functions.
- Example 2: URL Queries and Parsing JSON interacts with a simple web API to construct a full text data set of historic newspaper front pages.
- Example 3: Advanced APIs demonstrates using Jython to implement a POST request to a natural language processing web service.
Example 1: Fetching and Parsing HTML
This example downloads a single web page and parses it into a structured table using Refine’s built in functions. A similar workflow can be applied to a list of URLs, often generated by parsing another web page, creating a flexible web harvesting tool.
The raw data for this example is an HTML copy of Shakespeare’s Sonnets from Project Gutenberg. Processing a book of poems into structured data enables new ways of reading text, allowing us to sort, manipulate, and connect with other information.
Start “Sonnets” Project
Start OpenRefine and select Create Project. Refine can import data from a wide variety of formats and sources, from a local Excel file to web accessible RDF. One often over looked method is the Clipboard, which allows entering data via copy & paste. Under “Get Data From”, click Clipboard, and paste this URL into the text box:
Start project with clipboard
After clicking Next, Refine should automatically identify the content as a line-based text file and the default parsing options should be correct. Add the project name “Sonnets” at the top right and click Create project. This will result in a project with one column and one row.
Fetch HTML
Refine’s built-in function to retrieve a list of URLs is done by creating a new column. Click on the menu arrow of Column 1 > Edit column > Add column by fetching urls.
Edit column > Add column by fetching URL
Name the new column “fetch”. The Throttle delay option sets a pause time between requests to avoid being blocked by a server. The default is conservative.
Add column by fetch dialog box
After clicking “OK”, Refine will start requesting the URLs from the base column as if you were opening the pages in your browser, and will store each response in the cells of the new column. In this case, there is one URL in Column 1 resulting in one cell in the fetch column containing the full HTML source for the Sonnets web page.
Fetch results
Parse HTML
Much of the web page is not sonnet text and must be removed to create a clean data set. First, it is necessary to identify a pattern that can isolate the desired content. Items will often be nested in a unique container or given a meaningful class or id.
To make examining the HTML easier, click on the URL in Column 1 to open the link in a new tab, then right click on the page to “View Page Source”.
In this case the sonnets page does not have distinctive semantic markup, but each poem is contained inside a single
<p> element.
Thus, if all the paragraphs are selected, the sonnets can be extracted from the group.
Each sonnet is a <p> with lines separated by <br />
On the fetch column, click on the menu arrow > edit column > Add column based on this column. Give the new column the name “parse”, then click in the Expression text box.
Edit column > Add column based on this column
Data in Refine can be transformed using the General Refine Expression Language (GREL). The Expression box accepts GREL functions that will be applied to each cell in the existing column to create values for the new one. The Preview window below the Expression box displays the current value on the left and the value for the new column on the right.
The default expression is
value, the GREL variable representing the current contents of a cell.
This means that each cell is simply copied to the new column, which is reflected in the Preview.
GREL variables and functions are strung together in sequence using a period, called dot notation.
This allows complex operations to be constructed by passing the results of each function to the next.
GREL’s
parseHtml() function can read HTML content, allowing elements to be accessed using the
select() function and the jsoup selector syntax.
Starting with
value, add the functions
parseHtml() and
select("p") in the Expression box using dot notation, resulting in:
value.parseHtml().select("p")
Do not click OK at this point, simply look at the Preview to see the result of the expression.
Edit the GREL expression, parseHtml function
Notice that the output on the right no longer starts with the HTML root elements (
<!DOCTYPE html etc.) seen on the left.
Instead, it starts with a square bracket
[, displaying an array of all the
p elements found in the page.
Refine represents an array as a comma separated list enclosed in square brackets, for example
[ "one", "two", "three" ].
Refine is visual and iterative; it is common to gradually build up an expression while checking the preview to see the result. In addition to helping debug your GREL, this provides an opportunity learn more about the data set before adding more functions. Try the following GREL statements in the Expression box without clicking OK. Watch the preview window to understand how they function:
- Adding an index number to the expression selects one element from the array, for example
value.parseHtml().select("p")[0]. The beginning of the sonnets file contains many paragraphs of license information that are unnecessary for the data set. Skipping ahead through the index numbers, the first sonnet is found at
value.parseHtml().select("p")[37].
- GREL also supports using negative index numbers, thus
value.parseHtml().select("p")[-1]will return the last item in the array. Working backwards, the last sonnet is at index
[-3].
- Using these index numbers, it is possible to slice the array, extracting only the range of
pthat contain sonnets. Add the
slice()function to the expression to preview the sub-set:
value.parseHtml().select("p").slice(37,-2).
Clicking OK with the expression above will result in a blank column, a common cause of confusion when working with arrays.
Refine will not store an array object as a cell value.
It is necessary to use
toString() or
join() to convert the array into a string variable.
The
join() function concatenates an array with the specified separator.
For example, the expression
[ "one", "two", "three" ].join(";") will result in the string “one;two;three”.
Thus, the final expression to create the parse column is:
value.parseHtml().select("p").slice(37,-2).join("|")
Click OK to create the new column using the expression.
Split Cells
The parse column now contains all the sonnets separated by “|”, but the project still contains only one row.
Individual rows for each sonnet can be created by splitting the cell.
Click the menu arrow on the parse column > Edit cells > Split multi-valued cells.
Enter the separator
| that was used to
join in the last step.
Edit cells > Split multivalued cells
After this operation, the top of the project table should now read 154 rows. Below the number is an option toggle “Show as: rows records”. Clicking on records will group the rows based on the original table, in this case it will read 1. Keeping track of these numbers is an important “sanity check” when transforming data in Refine. The 154 rows make sense because the ebook contained 154 sonnets, while 1 record represents the original table with only one row. An unexpected number would indicate a problem with the transformation.
Project rows
Each cell in the parse column now contains one sonnet surround by a
<p> tag.
The tags can be cleaned up by parsing the HTML again.
Click on the parse column and select Edit cells > Transform.
This will bring up a dialog box similar to creating a new column.
Transform will overwrite the cells of the current column rather than creating a new one.
In the expression box, type
value.parseHtml().
The preview will show a complete HTML tree starting with the
<html> element.
It is important to note that
parseHtml() will automatically fill in missing tags, allowing it to parse these cell values despite not being valid HTML documents.
Select the
p tag, add an index number, and use the function
innerHtml() to extract the sonnet text:
value.parseHtml().select("p")[0].innerHtml()
Click OK to transform all 154 cells in the column.
Edit cells > Transform
selectreturns an array of
pelements even though there is only one in each cell. Attempting to pass an array to
innerHtml()will raise an error. Thus, an index number is necessary to select the first (and only) item in the array to pass the correct object type to
innerHtml().
Keep data object types in mind when debugging GREL expressions!
Unescape
Notice that each cell has dozens of
, an HTML entity used to represent “no-break space” since browsers ignore extra white space in the source.
These entities are common when harvesting web pages and can be quickly replaced with the corresponding plain text characters using the
unescape() function.
On the parse column, select Edit cells > Transform and type the following in the expression box:
value.unescape('html')
The entities will be replaced with normal whitespace.
Extract Information with Array Functions
GREL array functions provide a powerful way to manipulate text data and can be used to finish processing the sonnets.
Any string value can be turned into an array using the
split() function by providing the character or expression that separates the items (basically the opposite of
join()).
In the sonnets each line ends with
<br />, providing a convenient separator for splitting.
The expression
value.split("<br />") will create an array of the lines of each sonnet.
Index numbers and slices can then be used to populate new columns.
Keep in mind that Refine will not output an array directly to a cell.
Be sure to select one element from the array using an index number or convert it back to a string with
join().
Furthermore, the sonnet text contains a huge amount of unnecessary white space that was used to layout the poems in the ebook.
This can be cut from each line using the
trim() function.
Trim automatically removes all leading and trailing white space in a cell, an essential for data cleaning.
Using these concepts, a single line can be extracted and trimmed to create clean columns representing the sonnet number and first line. Create two new columns from the parse column using these names and expressions:
- “number”,
value.split("<br />")[0].trim()
- “first”,
value.split("<br />")[1].trim()
GREL split and trim
The next column to create is the full sonnet text which contains multiple lines.
However,
trim() will only clean the beginning and end of the cell, leaving unnecessary whitespace in the body of the sonnet.
To trim each line individually use the GREL control
forEach(), a handy loop that iterates over an array.
From the parse column, create a new column named “text”, and click in the Expression box.
A
forEach() statement asks for an array, a variable name, and an expression applied to the variable.
Following the form
forEach(array, variable, expression), construct the loop using these parameters:
- array:
value.split("<br />"), creates an array from the lines of the sonnet in each cell.
- variable:
line, each item in the array is then represented as the variable (it could be anything,
vis often used).
- expression:
line.trim(), each item is then evaluated separately with the specified expression. In this case,
trim()cleans the white space from each sonnet line in the array.
At this point, the statement should look like
forEach(value.split("<br />"), line, line.trim()) in the Expression box.
Notice that the Preview now shows an array where the first element is the sonnet number.
Since the results of the
forEach() are returned as a new array, additional array functions can be applied, such as slice and join.
Add
slice(1) to remove the sonnet number, and
join("\n") to concatenate the lines in to a string value (
\n is the symbol for new line in plain text).
Thus, the final expression to extract and clean the full sonnet text is:
forEach(value.split("<br />"), line, line.trim()).slice(1).join("\n")
GREL forEach expression
Click “OK” to create the column. Following the same technique, add another new column from parse named “last” to represent the final couplet lines using:
forEach(value.split("<br />"), line, line.trim()).slice(-3).join("\n")
Finally, numeric columns can be added using the
length() function.
Create new columns from text with the names and expressions below:
- “characters”,
value.length()
- “lines”,
value.split(/\n/).length()
Cleanup and Export
In this example, we used a number of operations to create new columns with clean data. This is a typical Refine workflow, allowing each transformation to be easily checked against the existing data. At this point the unnecessary columns can be removed. Click on the All column > Edit columns > Re-order / remove columns.
All > Edit columns
Drag unwanted column names to the right side of the dialog box, in this case Column 1, fetch, and parse. Drag the remaining columns into the desired order on the left side. Click Ok to remove and reorder the data set.
Re-order / Remove columns
Use filters and facets to explore and subset the collection of sonnets. Then click the export button to generate a version of the new sonnet table for use outside of Refine. Only the currently selected subset will be exported.
Export CSV
Example 2: URL Queries and Parsing JSON
Many cultural institutions provide web APIs allowing users to access information about their collections via simple HTTP requests. These sources enable new queries and aggregations of text that were previously impossible, cutting across boundaries of repositories and collections to support large scale analysis of both content and metadata. This example will harvest data from the Chronicling America project to assemble a small set of newspaper front pages with full text. Following a common web scraping workflow, Refine is used to construct the query URL, fetch the information, and parse the JSON response.
Start “Chronicling America” Project
To get started after completing Example 1, click the Open button in the upper right. A new tab will open with the Refine start project view. The tab with the Sonnets project can be left open without impacting performance. Create a project from Clipboard by pasting this CSV into the text box:
state,year Idaho,1865 Montana,1865 Oregon,1865 Washington,1865
After clicking Next, Refine should automatically identify the content as a CSV with the correct parsing options. Add the Project name “ChronAm” at the top right and click Create project.
Create project
Construct a Query
Chronicling America provides documentation for their API and URL patterns.
In addition to formal documentation, information about alternative formats and search API are sometimes given in the
<head> element of a web page.
Check for
<link rel="alternate",
<link rel="search", or
<!-- comments which provide hints on how to interact with the site.
These clues provide a recipe book for interacting with the server using public links.
The basic components of the ChromAm API are:
- the base URL,
- the search service location for individual newspaper pages,
search/pages/results
- a query string, starting with
?and made up of value pairs (
fieldname=value) separated by
&. Much like using the advanced search form, the value pairs of the query string set the search options.
Using a GREL expression, these components can be combined with the values in the “ChronAm” project to construct a search query URL.
The contents of the data table can be accessed using GREL variables.
As introduced in Example 1, the value of each cell in the current column is represented by
value.
Values in the same row can be retrieved using the
cells variable plus the column name.
There are two ways to write a
cells statement: bracket notation
cells['column name'].value which allows column names that include a space, or dot notation
cells.column_name.value which allows only single word column names.
In GREL, strings are concatenated using the plus sign.
For example, the expression
"one" + "two" would result in “onetwo”.
To create the set of search queries, from the state column, add a column named “url” with this expression:
"" + value.escape('url') + "&>IMAGE_17<<
Create query URL
The expression concatenates the constants (base URL, search service, and query field names) together with the values in each row.
The
escape() function is added to the cell variables to ensure the string will be safe in a URL (the opposite of the
unescape() function introduced in Example 1).
Look at the value pairs after the
? to understand the parameters of the search.
Explicitly, the first query URL will ask for newspapers:
- from Idaho (
state=Idaho)
- from the year 1865, (
date1=1865&date2=1865&dateFilterType=yearRange)
- only the front pages (
sequence=1)
- sorting by date (
sort=date)
- returning a maximum of five (
rows=5)
- in JSON (
format=json)
Fetch URLs
The url column is a list of web queries that could be accessed with a browser. To test, click one of the links. The url will open in a new tab, returning a JSON response.
Fetch the URLs using url column by selecting Edit column > Add column by fetching urls. Name the new column “fetch” and click OK. In a few seconds, the operation should complete and the fetch column will be filled with JSON data.
Parse JSON to Get Items
The first name/value pairs of the query response look like
"totalItems": 52, "endIndex": 5.
This indicates that the search resulted in 52 total items, but the response contains only five (since it was limited by the
rows=5 option).
The JSON key
items contains an array of the individual newspapers returned by the search.
To construct a orderly data set, it is necessary to parse the JSON and split each newspaper into its own row.
GREL’s
parseJson() function allows us to select a key name to retrieve the corresponding values.
Add a new column based on fetch with the name “items” and enter this expression:
value.parseJson()['items'].join("|||")
parse json items
Selecting
['items'] exposes the array of newspaper records nested inside the JSON response.
The
join() function concatenates the array with the given separator resulting in a string value.
Since the newspaper records contain an OCR text field, the strange separator “|||” is necessary to ensure that it is unique and can be used to split the values.
Split Multivalued Cells
With the individual newspapers isolated, separate rows can be created by splitting the cells.
On the items column, select Edit cells > Split multivalued cells, and enter the join used in the last step,
|||.
After the operation, the top of the project table should read 20 rows.
Clicking on Show as records should read 4, representing the original CSV rows.
Notice that the new rows are empty in all columns except items.
To ensure the state is available with each newspaper issue, the empty values can be filled using the
Fill down function.
Click on the state column > Edit cells > Fill down.
fill down
This is a good point to clean up the unnecessary columns. Click on the All column > Edit columns > Re-order / remove columns. Drag all columns except state and items to the right side, then click OK to remove them.
Re-order / remove columns
Sanity check: with the original columns removed, both records and rows will read 20. This makes sense, as the project started with four states and fetched five records for each.
Parse JSON Values
To complete the data set, it is necessary to parse each newspaper’s JSON record into individual columns.
This is a common task, as many web APIs return information in JSON format.
Again, GREL’s
parseJson() function makes this easy.
Create a new column from items for each newspaper metadata element by parsing the JSON and selecting the key:
- “date”,
value.parseJson()['date']
- “title”,
value.parseJson()['title']
- “city”,
value.parseJson()['city'].join(", ")
- “lccn”,
value.parseJson()['lccn']
- “text”,
value.parseJson()['ocr_eng']
After the desired information is extracted, the items column can be removed by selecting Edit column > Remove this column.
Final ChronAm project columns
Each column could be further refined using other GREL transformations.
For example, to convert date to a more readable format, use GREL date functions.
Transform the date column with the expression
value.toDate("yyyymmdd").toString("yyyy-MM-dd").
Another common workflow is to extend the data with further URL queries.
For example, a link to full information about each issue can be formed based on the lccn.
Create a new column based on lccn using the expression
"" + value + "/" + cells['date'].value + "/ed-1.json".
Fetching this URL returns a complete list of the issue’s pages, which could in turn be harvested.
For now, the headlines of 1865 from the Northwest are ready to enjoy!
Example 3: Advanced APIs
Example 2 demonstrated Refine’s fetch function with a simple web API, essentially utilizing URL patterns to request information from a server. This workflow uses the HTTP GET protocol, meaning the query is encoded in the URL string, thus limited in length (2048 ASCII characters), complexity, and security. Instead, many API services used to enhance text data, such as geocoding or named entity recognition, use HTTP POST to transfer information to the server for processing.
GREL does not have a built in function to use this type of API. However, the expression window language can be changed to Jython, providing a more complete scripting environment where it is possible to implement a POST request.
Jython is Python implemented for the Java VM and comes bundled with Refine. This means Python 2 scripts using the Standard Library can be written or loaded into the expression window, and Refine will apply them to each cell in the transformation. The official documentation is sparse, but the built-in Jython can be extended with non-standard libraries using a work around.
Keep in mind that spending time writing complex scripts moves away from the strengths of Refine. If it is necessary to develop a lengthy Jython routine, it will likely be more efficient to process the data directly in Python. On the other hand, if you know a handy method to process data in Python 2, Jython is a easy way to apply it in a Refine project.
Jython in the Expression Window
Return to the “Sonnets” project completed in Example 1. If the tab was closed, click Open > Open Project and find the Sonnets example (Refine saves everything for you!).
Add a new column based on the first column named “sentiment”. We will use this window to test out a series of expressions, so leave it open until we get to the final iteration of the request.
On the right side of the Expression box is a drop down to change the expression language. Select Python / Jython from the list.
Jython expression
Notice that the preview now shows
null for the output.
A Jython expression in Refine must have a
return statement to add the output to the new cells in the transformation.
Type
return value into the Expression box.
The preview will update showing the current cells copied to the output.
The basic GREL variables can be used in Jython by substituting brackets instead of periods.
For example, the GREL
cells.column-name.value would be Jython
cells['column-name']['value'].
Jython GET Request
To create a HTTP request in Jython, use the standard library urllib2. Refine’s fetch function can be recreated with Jython to demonstrate the basics of the library. In the expression box, type:
import urllib2 get = urllib2.urlopen("") return get.read()
Jython GET request
The preview should display the HTML source of the Jython home page, this is an HTTP GET request as in previous fetch examples.
Notice that similar to opening and reading a text file with Python,
urlopen() returns a file-like object that must be
read() into a string.
The URL could be replaced with cell variables to construct a query similar to the fetch used in Example 2.
POST Request
Urllib2 will automatically send a POST if data is added to the request object. For example, Text Processing provides natural language processing APIs based on Python NLTK. The documentation for the Sentiment Analysis service provides a base URL and the name of the key used for the data to be analyzed. No authentication is required and 1,000 calls per day are free for non-commercial use.2
This type of API is often demonstrated using curl on the commandline.
Text Processing gives the example
curl -d "text=great" which can be recreated in Jython to test the service.
Building on the GET expression above, the POST data is added as the second parameter of urlopen, thus the request will be in the form
urllib2.urlopen(url, data).
Type this script into the expression window:
import urllib2 url = "" data = "text=what is the sentiment of this sentence" post = urllib2.urlopen(url, data) return post.read()
The preview should show a JSON response with sentiment probability values. To retrieve sentiment analysis data for the first lines of the sonnets (remember we are still adding a column based on first!), put the basic Jython pattern together with the values of the cells:
import urllib2 url = "" data = "text=" + value post = urllib2.urlopen(url, data) return post.read()
jython request
Click OK and the Jython script will run for every row in the column.
The JSON response can then be parsed with GREL using the methods demonstrated in Example 2 (for example,
value.parseJson()['label']).
Given the small expression window and uniform data, the script above is pragmatically simplified and compressed.
When Refine is encountering problems, it is better to implement a more complete script with error handling.
If necessary, a throttle delay can be implemented by importing
time and adding
time.sleep() to the script.
For example, the POST request could be rewritten:
import urllib2, urllib, time time.sleep(15)
Some APIs require authentication tokens to be passed with the POST request as data or headers. Headers can be added as the third parameter of
urllib2.Request()similar to how data was added in the example above. Check the Python urllib2 documentation and how-to for advanced options.
When harvesting web content, character encoding issues commonly produce errors in Python. Trimming whitespace, using GREL
escape()/
unescape(), or Jython
encode("utf-8")will often fix the problem.
Compare Sentiment
To practice constructing a POST request, read the documentation for Sentiment Tool, another free API.
Find the service URL and data key necessary to modify the Jython pattern above.
Create a new column from first named
sentiment2 and test the script.
There are many possible ways to create the request, for example:
import urllib2 url = "" data = "txt=" + value post = urllib2.urlopen(url, data) return post.read()
The JSON response contains different metrics, but it will be obvious that the APIs disagree on many of the sentiment “labels” (for example, use
value.parseJson()['result']['sentiment'] to extract a label comparable to the first API).
These are simple free APIs for demonstration purposes, but it is important to critically investigate services to more fully understand the potential of the metrics.
Both APIs use a naive bayes classifier to categorize text input. These models must be trained on pre-labeled data and will be most accurate on similar content. Text Processing is trained on twitter and movie reviews3, and Sentiment Tool on IMDb movie reviews4. Thus both are optimized for small chunks of modern English language similar to a review, with a limited bag of words used to determine the sentiment probabilities.
Archaic words and phrases contribute significantly to the sonnets’ sentiment, yet are unlikely to be given any weight in these models since they are not present in the training data. While comparing the metrics is fascinating, neither is likely to produce quality results for this data set. Rather than an accurate sentiment, we might be surprised to find a quantifiable dissonance between the sonnet’s English and our modern web usage. However, a model optimized to Shakespeare’s words could be developed using more appropriate training data. To learn more about classifiers and how to implement one, see Vilja Hulden’s PH lesson “Supervised Classification: The Naive Bayesian Returns to the Old Bailey” or Steven Bird, Ewan Klein, and Edward Loper’s “Learning to Classify Text” in the NTLK Book.
Accessing data and services on the web opens new possibilities and efficiencies for humanities research. While powerful, these APIs are often not aimed at humanities scholarship and may not be appropriate or optimized for our inquiries. The training data may be incomplete, biased, or secret. We should always be asking questions about these aggregations and algorithms, thinking critically about the metrics they are capable of producing. This is not a new technical skill, but an application of the historian’s traditional expertise, not unlike interrogating physical primary materials to unravel bias and read between the lines. Humanities scholars routinely synthesize and evaluate convoluted sources to tell important narratives, and must carry that skill into digital realm. We can critically evaluate data sources, algorithms, and API services, as well as create new ones more suited to our questions and methods.
With its unique ability to interactively wrangle data from raw aggregation to analysis, Refine supports exploratory research and offers a wonderfully fluid and playful approach to tabular data. OpenRefine is a flexible, pragmatic tool that simplifies routine tasks and, when combined with domain knowledge, extends research capabilities.
David Huynh, “Google Refine”, Computer-Assisted Reporting Conference 2011,. ↩
As of July 2017, see API Documentation. ↩
Jacob Perkins, “Sentiment Analysis with Python NLTK Text Classification”,. ↩
Vivek Narayanan, Ishan Arora, and Arjun Bhatia, “Fast and accurate sentiment classification using an enhanced Naive Bayes model”, 2013, arXiv:1305.6143. ↩ | https://programminghistorian.org/en/lessons/fetch-and-parse-data-with-openrefine | CC-MAIN-2020-40 | refinedweb | 5,423 | 54.73 |
Back when Java was called Oak, it was thought that this new language would be ideal for developing embedded applications, such as those that would run on set-top boxes. The developers of this new language were well ahead of their time. Java's momentum began to build not from its large set-top developer community but from developers wishing to enhance their Web sites using Java applets. Thank goodness that was short-lived!
Java then became popular in server-side applications, but it has only recently begun to gain popularity in the embedded devices it was originally intended for. Java is now running on, and in, everything from big SMP servers to portable devices, such as PDAs, phones, and even smart cards.
Like many Java enthusiasts, I'm interested in exploring the capabilities of Java programs on small-footprint devices, especially my own Palm Pilot. Sometimes the best way to learn more about a new technology, or to develop a new skill, is to just mess around with stuff. Some refer to this as hacking (not to be confused with cracking, which is breaking into computer systems illegally).
Not too long ago I discovered plans for a Palm Pilot Robot at Carnegie Mellon University's School of Computer Science. I downloaded the plans, bought all the necessary parts (except for the Palm Pilot, which I already had), and started putting it together. After I got the robot assembled and sandwiched together, I immediately wanted to see if I could control it with a Java program.
I learned a great deal while hacking a few Java programs to control various parts of the Palm Pilot Robot Kit (PPRK) hardware, and much of what I learned can be applied directly to embedded applications.
For example, I decided to construct a simple framework that attempts to make programming robot software, for robots similar to the PPRK, much easier.
This article discusses the lessons learned in writing Java software to make this robot come alive - well, sort of alive.
Java programs running on your favorite handheld device can serve as the brains for your robot creation.
Waba
Today there are several Java, or Java-like, Virtual Machines (VMs) for running embedded Java applications. Waba is one such VM. The Waba SDK provides a Java-like development environment for small-footprint devices and is available under the terms of the GNU Public License (GPL). Because it's an open source VM implementation, a large group of developers continue to enhance and improve the Waba API on a project called SuperWaba.
I didn't do extensive research on what VM I wanted to use and run on my PPRK. I had some experience with Waba already and have found it easy to understand, download, and install. The fact that it's distributed under the GPL is also in its favor. Furthermore, the SuperWaba newsgroup is very active - and developers, such as Guihlerme Campos Hazan (lead SuperWaba developer), are friendly and quick to answer newbie developer's questions. These types of development communities make it easier to get up to speed on new and emerging technologies.
After assembling my PPRK (see Resources section) and choosing a VM for my Palm V that could run Java-like programs, I was ready to start writing some Java code.
It's All About the Serial Port
The key to writing a Waba application to control your Palm Pilot Robot is a good understanding of the following:
As an aside, if you decide to buy the PPRK kit from Acroname, which I recommend, this modified HotSync cable is provided for you in the kit. (Note: You can download a PDF version of the SV203 manual from to learn more about the SV203 design and protocol specifications.)
Understanding how to first send commands from your PC to your SV203 board using a serial cable (at your local Radio Shack) and a terminal emulation program is important. I have documented some notes and procedures on how to do this, as well as notes for debugging your PPRK hardware and software, at.
Communicating with the SV203 is quite simple. You need to tell the board what servo motor you wish to control and in what direction and speed you wish to move it. You do this by generating a string of ASCII characters that represent a command and the device number you wish to control, terminating the string with a "\r".
For example, the command SV1 M55 turns servo 1 counterclockwise (counterclockwise movement is any number between 0 and 127, and clockwise movement is any number between 128 and 255. Also note that the motors turn slower the farther away from 0 up to 127 you get, and faster the farther from 128 up to 255 you get).
Once you establish a connection between your SV203 and your PC's terminal emulation program (on Linux I use minicom), you can type the command above, hit return (enter), and servo motor 1 should begin a clockwise rotation. To stop the motor, enter the command SV1 M0 and hit return (enter).
The PPRK has three motors, so you can control all three by making the appropriate substitutions in the command sent to the SV203 board. Now all you need to figure out is how to write these same commands to the serial port in our Waba program.
Waba makes this easy to do. As mentioned earlier, Waba has a class in the waba.io package called SerialPort, which you'll use to open a connection to the SV203 controller board serial port. This class can be constructed in two ways:
SerialPort(int port_number, int baud_rate)
SerialPort(int port_number, int baud_rate,
int bits, boolean parity, int stopbits)
SerialPort sp = new SerialPort(0, 9600);
sp.setFlowControl(false);
byte[] buff = new byte[7];
buff[0] = (byte)'S';
buff[1] = (byte)'V';
buff[2] = 49;
// ASCII equivalent of 1.
Very important!
buff[3] = (byte)'M';
buff[4] = 53;
// ASCII equivalent of 5.
buff[5] = 53;
buff[6] = (byte)'\r';
// End of command
sp.writeBytes(buff, 0, 7)
Give the Gift of Sight
The PPRK uses three Sharp GP2D12 Infrared Object Detectors, which are also connected to your SV203 board. These little infrared sensors are used to detect nearby objects. The GP2D12 IR sensor will change the voltage on a given SV203 port, based on the distance, in centimeters, a given object is from the sensor. You communicate with these sensors the same way you communicate with the servos, except this time you must also read a 4-byte response from the board. The SV203 protocol for sending a request to the IR sensor is simply to send the following ASCII command: AD1\r. This tells the SV203 board to take a reading from the first IR sensor and to send 4 bytes back to our Palm device indicating the range, in centimeters, of the closest object, if any. You can create a 4-byte array and populate it with the command like so:
byte buff[] = new byte[4];
buff[0] = (byte)'A';
buff[1] = (byte)'D';
buff[2] = 49; // ASCII equivalent of 1.
buff[3] = (byte)'\r';
sp.writeBytes(buff, 0, 4);
waba.sys.Vm.sleep(15);
Label lblIRVal = new Label("");
sp.readBytes(buff, 0, 4);
StringBuffer sbsensorin = new StringBuffer();
for (int i=0;i<4; i++) {
if ( ( buff[i] != 0x0 ) && ( buff[i]
!= (byte)13 ) && (buff[i] != (byte)10 ) )
sbsensorin.append( (char) buff[i] );
}
lblIRVal.setText( sbsensorin.toString());
One of the truly neat things about Waba is the availability of the Waba VM on several different embedded platforms, such as Palm, iPaq, Apple's Newton, and even DOS. While I have not tested the portability of WORF across these platforms, it's certainly conceivable that robots can be built using any of these devices and powered with Waba programs built on top of WORF.
The PPRK consists of three servo motors, three GP2D12 infrared sensors, and a Pontech SV203 Controller Board to coordinate and control these devices. WORF, therefore, consists of Java components for each, and provides a burgeoning API set for easily sending messages to the SV203 board on behalf of a given component. The utils package provides miscellaneous support functions (see Figure 1).
With WORF, developers of embedded robot software applications can focus more on the creative aspects of what they want their robot to do and less on the details of how to communicate with this specific type of hardware. This is accomplished by encapsulating the details of sending the specific commands described earlier to the SV203 board and making this functionality available vis-á-vis an easy-to-use set of APIs.
SV203 Component
The SV203 Waba component extends, or subclasses, the waba.io.SerialPort class and provides three constructors, each of which provides the developer with a different means of initializing the parent SerialPort class. The SV203 Waba component maps to the Pontech SV203 controller board piece of hardware. The best reason to morph the waba.io.SerialPort class into the SV203 class, rather than just use the SerialPort object provided by Waba, was the need to wait at least 3 milliseconds for the SV203 board to process commands that require a response. While this sleep could just as easily have been put in the IRSensor class, there was also the aesthetic reason to have an SV203 Waba component that could easily be paired with the SV203 hardware component. Using this Waba component as a fundamental building block of the other two, the servo and IR components can easily wrap convenient API calls around the lower-level serial port writes and reads employed by the SV203 Waba component.
Servo Component
The PPRKServo component takes an instance of the SV203 object as an argument to its constructor. As a result, the PPRK Servo component implements easy-to-use APIs, like turnRight, turnLeft, stop, moveServo, and moveHolonomic. These APIs, in turn, stuff a byte array with the appropriate ASCII commands and call the appropriate write method on the SV203 instance.
IR Component
The IRSensor component also takes an instance of SV203 as an argument to its single constructor. As stated earlier, when communicating with the GP2D12, a response is expected from the SV203 controller board with each command sent to it requesting object location information. The IRSensor component implements methods to poll a particular IR sensor for a data reading and also includes methods getStringPortValue and getIntPortValue, which return the IR sensor readings as either an int or a string.
Utilities
Finally, WORF currently uses a simple class, Utils, to provide static functions for byte-to-ASCII conversions, and vice versa. It's meant to be a catch-all class for methods that don't really fit anywhere else.
Putting It All Together
Okay, so here you are with our PPRK hardware all assembled and functioning (see Resources for WORF diagnostic utilities and hardware troubleshooting tips), and you have a basic knowledge of how to develop for the robot. But what can you do with it?
Well, at the risk of using a cliché, you're truly limited only by your imagination, creativity, and attention span to your project.
My first idea was an attempt to make my PPRK do a Mexican Hat Dance by writing a short program using WORF. Listing 1 is the complete source code for my WORF Mexican Hat Dance application, which you can run on your own PPRK (see Figure 2).
This is a simple demonstration of how easy it is to write a small robot program for your PPRK using WORF. The WORFHatDance application (see Resources) causes the robot to alternately turn right and left at different stages of the musical ditty it plays when you tap the Push Me button displayed on your Palm (see Figure 3). The static waba.fx.Sound.tone() method tells your Waba application to play a tone at the given frequency for the given duration. The tones specified in Listing 1 play some semblance of the Mexican Hat Dance, even if it is a little off key at times.
I'm sure many reading this article are asking themselves, "What's the real value in building a PPRK and writing software for it? Could I enter my PPRK in the BattleBots competition? More important, how can I make money with it?" The real value in these types of exercises, however, is fun and education. Granted, the PPRK, as it is, probably couldn't easily be modified to do your laundry or sweep your floor, and wouldn't last two seconds in the BattleBots arena. The servo motors aren't strong and the GP2D12 IR sensors are somewhat delicate.
But I have to admit to a certain childlike fascination in writing a few lines of code capable of controlling hardware external to my Palm device. The PPRK provides a good platform for investigating possibilities in controlling and interacting with robotic hardware from a small footprint device, such as a Palm or iPaq. As far as I'm concerned, building robots and controlling them with my Java programs is just good fun!
The money will come, hopefully, from the knowledge you gain from basic projects such as this, strengthening your skills in embedded device programming, and contributing code - and lessons you've learned - to the Java development community at large.
Resources
Author Bio
James Caple is an independent programmer
and author. He has more than eight years
of industry experience, including building
mobile device synchronization software
and systems in Java. He is a Sun Java 2
certified programmer and developer.
Listing 1
package com.trexlabs.worf.robot;
import com.trexlabs.worf.sv203.*;
import com.trexlabs.worf.ir.*;
import com.trexlabs.worf.servo.*;
import waba.ui.*;
import waba.fx.*;
import waba.io.*;
/**
* An example program using WORF to make your robot dance while it
* plays a catchy tune.
*
*/
public class WORFHatDance extends MainWindow {
private Button begin;
private SV203 board;
private PPRKServo servos;
public WORFHatDance() {
begin = new Button("Let's Dance!");
begin.setRect(50, 85, 59, 20);
add(begin);
// WORF Setup
board = new SV203();
servos = new PPRKServo(board);
}
/**
* Draw about Strings.
* @param Graphics
* @return void
*/
public void onPaint( Graphics g ) {
g.setColor(0, 0, 0);
g.drawText("WORF Hat Dance Example", 0, 0);
g.drawText("Copyright (C) 2001, James Caple", 0, 10);
g.drawText("", 0, 20);
}
public void onEvent(Event evt) {
if (evt.type == ControlEvent.PRESSED && evt.target == begin) {
getYourGrooveOn();
}
}
private void getYourGrooveOn() {
// Swing to your right
servos.turnRight((byte)3);
Sound.tone(3000, 500);
Sound.tone(2900, 200);
Sound.tone(3000, 200);
Sound.tone(2600, 200);
Sound.tone(2500, 200);
Sound.tone(2600, 200);
Sound.tone(2100, 200);
Sound.tone(2000, 200);
Sound.tone(2100, 200);
Sound.tone(1500, 500);
// Swing to your left
servos.turnLeft((byte)3);
Sound.tone(1300, 200);
Sound.tone(1400, 200);
Sound.tone(1500, 200);
Sound.tone(1700, 200);
Sound.tone(1900, 200);
Sound.tone(2000, 200);
Sound.tone(2300, 200);
Sound.tone(2500, 200);
Sound.tone(2700, 200);
Sound.tone(2300, 500);
// Swing to your right
servos.turnRight((byte)3);
Sound.tone(2700, 200);
Sound.tone(2600, 200);
Sound.tone(2700, 200);
Sound.tone(2300, 200);
Sound.tone(2200, 200);
Sound.tone(2300, 200);
Sound.tone(1900, 200);
Sound.tone(1800, 200);
Sound.tone(1900, 200);
Sound.tone(1500, 500);
// Swing to your right
servos.turnLeft((byte)3);
Sound.tone(3000, 200);
Sound.tone(3000, 200);
Sound.tone(3000, 200);
Sound.tone(3300, 200);
Sound.tone(3000, 200);
Sound.tone(2700, 200);
Sound.tone(2500, 200);
Sound.tone(2200, 200);
Sound.tone(2000, 500);
Sound.tone(4000, 100);
// Cha cha cha!
servos.stop();
servos.turnRight((byte)3);
servos.turnLeft((byte)3);
servos.turnRight((byte)3);
servos.stop();
}
} | http://www2.sys-con.com/itsg/virtualcd/java/archives/0612/caple/index.html | CC-MAIN-2018-51 | refinedweb | 2,606 | 64.3 |
utimes − set file access and modification times (LEGACY)
#include <sys/time.h>
int utimes(const char *path, const struct timeval times[2]);
The utimes() function shall set shall be set to the current time. The effective user ID of the process shall match the owner of the file, or has write access to the file or appropriate privileges to use this call in this manner. Upon completion, utimes() shall mark the time of the last file status change, st_ctime, for update.
Upon successful completion, 0 shall be returned. Otherwise, -1 shall be returned and errno shall be set to indicate the error, and the file times shall not be affected.
The utimes() function shall fail if:
ENAMETOOLONG
The length of the path argument exceeds {PATH_MAX} or a pathname component is longer than {NAME_MAX}.
ENOTDIR
A component of the path prefix is not a directory.
The utimes() function may fail if:
ENAMETOOLONG
Pathname resolution of a symbolic link produced an intermediate result whose length exceeds {PATH_MAX}.
The following sections are informative.
None.
For applications portability, the utime() function should be used to set file access and modification times instead of utimes().
None.
This function may be withdrawn in a future version.
utime() , the Base Definitions volume of IEEE Std 1003.1-2001, . | http://man.cx/utimes(3) | CC-MAIN-2013-20 | refinedweb | 211 | 63.9 |
<<
import xlxs file to MySQL using PHP
Started by zerickdeguzman, Mar 05 2012 06:13 PMmysql import
2 replies to this topic
#1
Posted 05 March 2012 - 06:13 PM
I just want to ask if it is possible to import .xlsx file into MySQL using PHP without converting into csv? Thanks
- 0
Recommended for you: Get network issues from WhatsUp Gold. Not end users.
#2
Posted 05 March 2012 - 06:21 PM
PHP has a module for reading Excel files. I don't recall if it supports the XLSX format or just XLS.
- 0
Programming is a branch of mathematics.
My CodeCall Blog | My Personal Blog
My MineCraft server site:
#3
Posted 05 March 2012 - 06:37 PM
thanks
- 0
Also tagged with one or more of these keywords: mysql, import
Recommended from our users: Dynamic Network Monitoring from WhatsUp Gold from IPSwitch. Free Download | http://forum.codecall.net/topic/68601-import-xlxs-file-to-mysql-using-php/ | CC-MAIN-2019-51 | refinedweb | 146 | 70.53 |
« Example of the Flex Component Kit for Flash CS3 | Main | Adobe® Flex™ 3 Public Beta and Adobe® AIR™ »
June 07, 2007
Flex, Apollo, and Flash CS3
The Flex/Flash/Apollo Project
I've been at my latest project for a while, writing bits and pieces of it when I've gotten a chance. Since the Flash CS3 Flex Component kit was announced I've wanted to build something that used it. I had the idea of making an Apollo application to show that the kit wasn't just for Flex. Then I had a better idea: write an application for both Apollo and Flex, using Flash CS3 Flex Component Kit as well as a Flex Library Project to tie everything together.
I made what is perhaps a simple or silly application, but it does show how to do a number of different things. I call it the Flickr Scrapbook. The idea is that you make a scrapbook for your friends and family using photographs from Flickr - ideally your own photos, but anything public can be displayed. Each page can hold multiple photographs with captions and notes can be added as well. The pages and text can be colored, the photographs rotated and resized, and the whole thing can be displayed on a web page using Ely's FlexBook control.
The project is two applications. One is written for Apollo and is the Scrapbook Editor. The other is written for Flex and is the Scrapbook Viewer. It seemed appropriate that an editor would be written as an Apollo application because you may want to save your work onto your local machine. The viewer would of course, be on a web page so Flex was the obvious choice. I also created a Flex Library project to keep the common classes they both use. I used Flash CS3 to make skins and components that would be difficult in Flex alone.
You can view a couple scrapbooks I made by following these links:
If you have the Apollo runtime (labs.adobe.com/apollo) you can download the Scrapbook Editor and try it out:
Scrapbook AIR (scrapbook.air)
(note: you may be asked to save the file as a .zip - do not do that - rename the file with a .air extension)
Disclaimer
Aside from the usual, "use at your own risk, this is not supported by Adobe, no animals were harmed in the making of this application, etc. etc." disclaimers, I have to emphasize that I am NOT a developer. So my architecture may not be what you are used to. I know I didn't use enough interfaces to make software gurus swoon, but I think there is enough substance to at least give you ideas and to show you how to do things with Flex.
Source Code
The link here will download a zip file. The zip file contains everything: the source to both projects, the Flash CS3 source, and the Scrapbook Flex library project. You should be able to import the projects right into Flex Builder 2. If you have later version of Flex Builder, create new projects and just import the source files.
Bits and Pieces
- Use these two applications as a resource. Here are some things you'll find as you explore them:
- Reading and Writing Files using the Apollo File class. This class is so cool. It is cross-platform and easy to use.
- Making data service calls with HTTPService. I used my own Flickr API, but the one from Adobe Labs is cool too. I would have used that one but I had already started down my own path.
- Displaying Images. Using the Image tag is relatively straightforward. But mostly you'll want to show something while the image is loading and then switch to the image once it has loaded. I used Alex Uhlmann's "Flip" effect to spin the images into view.
- Using States and Transitions. This is one of the neatest features of Flex. I use states in several places, but if you start the Editor and start selecting things like photographs, notes, and the cover page, you'll see the property panels slide in and out. Hiding and showing the property area in the Editor is also a state change.
- Using Effects. As I just mentioned, I use effects to show the images, to switch property panels, among other things.
- Using Drag and Drop with the DragManager. Components like the DataGrid and Tree have drag and drop capability built in. I show you how to use it when that isn't available - just drag a photograph onto a scrapbook page and see.
- Making Flex Components and Skins with Flash CS3. Finally, Flash is in its rightful place along side Flex. I use the Flex Component Kit for Flash CS3 two ways: to make actual components (eg, the handle to hide and show the property area) and skins (most of the buttons).
- Creating and Using Custom Events. You can't write a decent application without custom events. And they are pretty easy, too.
- Using Cascading Style Sheets. I tried to put most of the styles into an external style sheet.
- Interaction Using the Mouse: Drag, Resize, and Rotate. Dragging things around the screen is very helpful with an editor. I show you how to do that along with resizing and rotating the photographs - using effects no less.
- Using Embedded Fonts. You must use embedded fonts if you want to scale text or modify it in any graphical way.
- Creating Components using ActionScript. Laying out your application using MXML tags is great, but it makes your application static. You'll need to know how to create and add components while the application is running. An example is creating a new photograph on a scrapbook page.
- Deploying Flex Applications to a Web Server. Once you've made your scrapbook file you need to put it to your webserver for people to see.
- Using a Custom HTML Wrapper. The Scrapbook Viewer uses a custom HTML wrapper which takes reads the scrapbook file name from the URL (query parameter) and passes it to the Flex application.
- Subclassing Components and Using Interfaces. You need to do this to get mileage out of your components. No need to write everything twice when you can extend something.
The majority of these items are found in the Scrapbook Editor. The Srapbook Viewer makes use of a few of the techniques and if you are interested in Ely's FlexBook, the Scrapbook Viewer code shows how to use it.
Here's an example of what you'll find in the code: I created the ActionScript class Photograph to encapsulate all the things a photograph on a scrapbook page can be. The Photograph class has properties such as the URL to the image on Flickr, the caption with the photograph, its rotation, its placement on the page, and so forth. However, that's not enough for either the Editor or the Viewer. In the Editor I want you to be able to select a photograph and use the mouse to resize it, rotate it, and delete it. In the Viewer I want you to click it to enlarge it.
To do those things I put the Photograph class in the Flex Library project to be used as the base class for both applications. Then I created the EditorPhotograph class for the Editor application and added the extras (resizing, rotation, etc). I did a similar thing with the Viewer.
There is also an example of an interface. A page in the scrapbook can hold two types of objects: Photographs and Notes. I wanted to write code as cleanly as possible and not be burdened with figuring out what type of object it had. This is a good place for an interface and I created the IScrapbookItem interface (also in the Flex Library project). Both Photographs and Notes implement it. The Editor extends that with IEditorItem as its needs a few extra things.
Scrapbook Editor Instructions
When you start the Scrapbook Editor you'll see two main areas: the one on the left is where your Flickr search results appear; the area on the right is where you build the scrapbook, page by page.
Begin by entering some tags (separated by commas) into the search box at the top left. Try simply miami beach and press Enter. After a bit of searching a page of images will appear.
Now give your scrapbook at title. Just enter the new title into the text box below the cover page.
You need a scrapbook page to place photos, so use the large green plus-sign above the scrapbook area to add a page. The page will be placed after the page you are viewing.
Now you can drag photos over to the page and drop them in place. The photos will become selected with the non-selected photos dimmed.
When a photograph is selected you can change its properties. Use the controls on the photograph to delete it, resize it, or rotate it. Below the page are other properties.
Click on the background of the page to de-select the photograph and the properties change to allow you to work with the page itself.
Continue to add pages and photographs. When are ready to save your work, use the File menu above the scrapbook. Select Save, locate a place, and give your file a name; the file's name will be changed to add .xml as the extension.
Deploying the Scrapbook
When you are ready to show the scrapbook to the world, copy the scrapbook .xml file you made, along with the contents of the deployment directory, to your web server. Send a URL to your friends and family:
Adding the query string, book=miami_vacation.xml will automatically load that scrapbook file into the viewer.
Things to To Do
As you use these applications you may find yourself asking why this or that feature is missing. Well, I wanted to get this project done so I left some things out and I wanted to give the 'interested reader' the opportunity to modify the code. Here's some items I'd like to see added and I may get around to doing them myself some day:
- You can add photographs from Flickr to your scrapbook. It would be nice to use photographs that are already on your computer, too.
- How about adding video clips? Imaging flipping to a page and there's a clip of you on the beach. Or may be not.
- It would be nice to add more properties for the title and notes fields such as size and font family.
- It would be nice to rotate and resize the notes on the scrapbook pages.
- You should be able to add textures to pages. Actually, some of the code is already there and needs to be finished.
- You should be able to add photographs and additional text to your scrapbook cover.
- It would be nice to add gradient fills to the scrapbook cover; may be the pages, too.
- It would be cool to have transparent pages. Check out Ely's FlexBook demo and the medical text book example.
- It would be nice to view thumbnails of the scrapbook pages in the editor so you could re-arrange them (or delete them).
- Right now in the Scrapbook Viewer, clicking on a photograph zooms it up on the current page. It would be nice if the photograph spanned the pages and could become larger.
This list could probably go on and on. But you get the idea - even if you don't want a scrapbook editor or viewer, this should provide you with a good opportunity to explore and try some things out. I hope the comments in the code are helpful enough to guide through these applications.
Summary
The time is right to put these technologies together. You can really make the experience matter.
Posted by pent at June 7, 2007 09:22 PM
Very solid code and application looks cool too!
It seems to me that you forgot to include in source files custom transition effects from namespace
"com.adobe.ac.mxeffects".
-----------------
Peter: You can get those classes from Alex Uhlmann's blog:
Posted by: JabbyPanda at June 13, 2007 05:05 AM
Thanks Peter for an answer, I already had figured out the location of AnimationPackage classes by myself.
My idea is that the application itself and the code architecture underneath is so good, that I advise you to take part in Adobe Apollo Derby, this app is a very solid candidate for the win.
What are license limitations of your code? Can I reuse certain ideas (XML data serialization, custom drag and drop support, most important - some, I stress it, some UI decisitions) in my commercial app?
If you want, we can continue this discussion via emails.
----------------------
Peter: I keep meaning to make the license more explicit. You can use this code for free, no royalties, etc. at your own risk. Meaning that Adobe doesn't support the code and I will try when I have time.
Posted by: JabbyPanda at June 15, 2007 07:20 AM
Downloaded Adobe AIR and tried running the Scrapbook.air install but I get this error:
This application could not be installed or launched (AIR file [path]Scrapbook.air is invalid: This application requires a version of the Adobe Integrated Runtime (AIR) which is no longer supported. Please contact the application author for an updated version.).
----------------
Peter: My timing on this wasn't so good. Shortly after releasing my examples we (Adobe) announced Flex Builder 3 Beta and Adobe AIR. The Adobe AIR is a newer version of my example. I posted a link a few days ago with an update, so try that. You can also go to my personal site, and download the application there.
Posted by: Nate at June 15, 2007 09:59 AM
Peter... this is fantastic. Thanks so much for sharing it. It has given me so much insight into how to properly structure things.
Nice job!
---------------
Peter: Thanks!
Posted by: Ben at July 6, 2007 05:39 PM
Hey Peter!
Quite informative post. We use Flash Flex Apollo in our web activities and believe that it is the best we can desire at the moment… nevertheless it is a common fact that technologies never stand frozen, the developing and updating every single moment - so we will wait for more news from Adobe :)
thanx a lot for sgaring useful information!
appreciated!
Posted by: Flash Flex Apollo at July 24, 2007 05:57 AM
Hi all,
I already use the flexbook component, and I'd like to use some of your code but can't find how these two brilliant pieces of code are working together.
Is there a place where you call the flexbook component in your code ?
Thanks for you help.
-----------------
Peter: If you look Layout.mxml you'll see the function handleResult. Inside of that function I create the FlexBook in ActionScript and then add all of the pages to it there.
Posted by: n1c0 at July 25, 2007 06:04 AM
I deployed the scrapbook viewer on my local server(WAMP). I tried the sample books successfully but none of images appear in book - just show "loading...", and my local server got an error.Anyone tell me wh
______________
Peter: You need to deploy the PHP code on your server. The PHP code makes the request to Flickr for the images and then sends them back to the Flex app (scrapbook viewer). The reason is that Flickr has no crossdomain.xml file on its servers and the Flex app requires authorization to do some of the bitmap tricks to make the FlexBook control work.
Posted by: Gyroly at August 13, 2007 03:17 AM
Super awesome! Looks like the goofy microsoft page flipper thing is nothing compared to this (that ms page flipper thing, while looking halfway neet, is completely impractical)
Posted by: Doctor at October 28, 2007 07:22?
Posted by: spinglitter at November 8, 2007 05:11?
Whoops, sorry , Peter - I just found the reply you wrote to Jabbypanda which deals with the same issue.
Posted by: spinglitter at November 8, 2007 05:14 AM
I am still intending to bring this up to date with Flex 3 Beta 2.
Posted by: Peter Ent at November 8, 2007 11:53 AM
I have been trying to get the Scrapbook Editor to work in both FlexBuilder 2 and 3 beta 2. I give up. I would sincerely appreciate any help you can provide.
thanks,
Steven
------------
I haven't done the port yet myself but I'll look into it for Beta 3.
Posted by: Steven Rubenstein at January 14, 2008 03:26 PM | http://weblogs.macromedia.com/pent/archives/2007/06/flex_apollo_and.cfm | crawl-002 | refinedweb | 2,791 | 73.17 |
CodePlexProject Hosting for Open Source Software
Hi,
I am stuck with a simple Problem. I want to "port" the BasicMVVMQuickStart from Silverlight to WPF. I've Setup a new Project, imported files and references but can't get over a build error that states that the dependency from
System.Windows, Version=2.0.5.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e"
can't be resolved. I know thats a Silverlight assembly. I have a couple of copies of that dll but None with that version number and referencing one of these lead to another bunch of Errors due to double referencing.
Does anybody know where to find that specific Version of System.Windows.dll?
Regards,
Peter
Hi Peter,
As far as we know not all assemblies provide the ability to run on both Silverlight
and .NET runtimes. For example this could be the case of the
System.Windows.dll used in Silverlight applications. For more information about the binary compatibility support between
Silverlight and WPF you can check the following article:
Take into account that porting from one platform to the other might not always be straightforward as some features may not be available for both platforms and because of the differences between the
XAML in Silverlight and WPF. In some cases you may have to change the namespace used in your
Silverlight application to match the WPF equivalents. An example of this could be the
VisualStateManager class which in Silverlight
can be located in the System.Windows.dll assembly but its
WPF version is defined in the PresentationFramework.dll assembly.
You can find more detailed information about these differences in the following resources:
So far, we have been able to port the Basic MVVM QuickStart from
Silverlight to WPF following this:
Create a new WPF project named BasicMVVMApp. This is the same as name of the namespace used in the Basic MVVM QuickStart's classes. (You can name you
WPF project with a different name, but then you will have to change the namespace of the aforementioned classes manually.)
Add a reference to Microsoft.Practices.Prism
Modify the App.xaml to add the following resources:
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="Theme/Theme.xaml"/>
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
Create two new folders in your WPF project, named Images and
Theme.
Import the following files of the original Basic MVVM QuickStart:
Open your MainWindow.xaml window and replace its XAML code with the contents of the
MainPage.xaml view of the original Basic MVVM QuickStart, including the namespaces. You should replace everything except for the
x:Class attribute of the MainWindow.xaml window.
Open the Theme.xaml file you imported before, and remove the following namespace:
Then, find any references to the aforementioned namespace inside this file and change them to use the default namespace which is set to use the
PresentationFramework.dll assembly. For example, you have to change:
<vsm:VisualStateManager.VisualStateGroups>
<!-- to: -->
<VisualStateManager.VisualStateGroups>
Finally, find the following styles inside the Theme.xaml file and change their
x:Name attribute to x:Key. This is because
Silverlight supports an x:Name on a ResourceDictionary item and can use
x:Name as a substitute for x:Key. However,
WPF does not support this behavior, and you have to use an x:Key instead.
I hope you find this useful,
Damian Cherubini
Hi Damian,
That was really helpful - thanks a lot (I probably wouldn't have figured out all the differences by myself and would probably have given up on this sample).
Kind regards,
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Core Graphics Tutorial: Arcs and Paths!
Version
- Swift 4.2, iOS 12, Xcode 10
Welcome back to another tutorial in our Core Graphics tutorial series! This series covers how to get started with Core Graphics. Core Graphics is a two-dimensional drawing engine with path-based drawing that helps you to create rich UIs.!
Getting Started
For this tutorial, you’ll use LearningAgenda, an iOS app that lists the tutorials you want to learn and the ones you’ve already learned.
Start by downloading the starter project using the Download Materials button at the top or bottom of this tutorial. Once downloaded, open LearningAgenda.xcodeproj in Xcode.
To keep you focused, the starter project has everything unrelated to arcs and paths already set up for you.
Build and run the app, and you’ll see the following initial screen:
As you can see, there is a grouped table consisting of two sections, each with a title and three rows. All the work you’re going to do here will create arced footers below each section.
Enhancing the Footer
Before taking on your challenge, you need to create and set up a custom footer that will behave as the placeholder for your future work.
To create the class for your shiny new footer, right-click the LearningAgenda folder and select New File. Next, choose Swift File and name the file CustomFooter.swift.
Switch over to CustomFooter.swift file and replace its content with the following code:
import UIKit class CustomFooter: UIView { override init(frame: CGRect) { super.init(frame: frame) isOpaque = true backgroundColor = .clear } required init?(coder aDecoder: NSCoder) { fatalError("init(coder:) has not been implemented") } override func draw(_ rect: CGRect) { let context = UIGraphicsGetCurrentContext()! UIColor.red.setFill() context.fill(bounds) } }
Here, you override
init(frame:) to set
isOpaquetrue. You also set the background color to clear.
isOpaqueproperty should not be used when the view is fully or partially transparent. Otherwise, the results could be unpredictable.
You also override
init?(coder:) since it’s mandatory, but you don’t provide any implementation since you will not create your custom footer in Interface Builder.
draw(_:) provides a custom rect content using Core Graphics. You set red as the fill color to cover the entire bounds of the footer itself.
Now, open TutorialsViewController.swift and add the following two methods to the
UITableViewDelegate extension at the bottom of the file:
func tableView(_ tableView: UITableView, heightForFooterInSection section: Int) -> CGFloat { return 30 } func tableView(_ tableView: UITableView, viewForFooterInSection section: Int) -> UIView? { return CustomFooter() }
The above methods combine to form a custom footer of 30 points in height.
Build and run the project and, if all works well, you should see the following:
Back to Business
OK, now that you have a placeholder view in place, it’s time to pretty it up. But first, here’s an idea of what you’re going for.
Note the following about the image above:
- The footer has a neat arc on the bottom.
- A gradient, from light gray to darker gray, is applied to the footer.
- A shadow fits the curve of the arc.
The Math Behind Arcs
An arc is a curved line that represents a part of a circle. In your case, the arc you want for the bottom of the footer is the top bit of a very large circle, with a very large radius, from a certain start angle to a certain end angle.
So how do you describe this arc to Core Graphics? Well, the API that you’re going to use is called
addArc(center:radius:startAngle:endAngle:clockwise:), an instance method of
CGContext. The method expects the following five inputs:
- The center point of the circle.
- The radius of the circle.
- The starting point of the line to draw, also know as the start angle.
- The ending point of the line to draw, also known as the end angle.
- The direction in which the arc is created.
But darn. Basically, this theorem states that, if you draw two intersecting chords in a circle, the product of the line segments of the first chord will be equal to the product of the segments of the second chord. Remember, a chord is a line that connects two points in a circle.
Armed with these two bits of knowledge, look what happens if you draw two chords like the following:
So, draw one line connecting the bottom points of your arc rect and another line from the top of the arc down to the bottom of the circle.
If you do that, you know a, b, and c, which lets you figure out d.
So d would be: (a * b) / c. Substituting that out, it’s:
// Just substituting... let d = ((arcRectWidth / 2) * (arcRectWidth / 2)) / (arcRectHeight); // Or more simply... let d = pow(arcRectWidth, 2) / (4 * arcRectHeight);
And now that you know c and d, you can calculate the radius with the following formula: (c + d) / 2:
// Just substituting... let radius = (arcRectHeight + (pow(arcRectWidth, 2) / (4 * arcRectHeight))) / 2; // Or more simply... let radius = (arcRectHeight / 2) + (pow(arcRectWidth, 2) / (8 * arcRectHeight));
Nice! Now that you know the radius, you can get the center by simply subtracting the radius from the center point of your shadow rect:
let arcCenter = CGPoint(arcRectTopMiddleX, arcRectTopMiddleY - radius)
Once you know the center point, radius and arc rect, you can compute the start and end angles with a bit of trigonometry:
You’ll start by figuring out the angle shown in the diagram, here. If you remember SOHCAHTOA, you might recall the cosine of an angle equals the length of the adjacent edge of the triangle divided by the length of the hypotenuse.
In other words,
cosine(angle) = (arcRectWidth / 2) / radius. So, to get the angle, you simply take the arc-cosine, which is the inverse of the cosine:
let angle = acos((arcRectWidth / 2) / radius)
And now that you know that angle, getting the start and end angles should be rather simple:
Nice! Now that you understand how, you can put it all together as a function.
addArc(tangent1End:tangent2End:radius:)method available in
CGContexttype.
Drawing Arcs and Creating Paths
The first thing you add is a way to convert degrees to radians. To do it, you’ll use the Foundation Units and Measurements APIs introduced by Apple in iOS 10 and macOS 10.12.
Open Extensions.swift and paste the following code at the end of the file:
typealias Angle = Measurement<UnitAngle> extension Measurement where UnitType == UnitAngle { init(degrees: Double) { self.init(value: degrees, unit: .degrees) } func toRadians() -> Double { return converted(to: .radians).value } }
In the code above, you define an extension on the
Measurement type restricting its usage to angle units.
init(degrees:) only works with angles in terms of degrees.
toRadians() allows you to convert degrees to radiants.
radians = degrees * π / 180.
Remaining in Extensions.swift file, find the extension block for
CGContext. Before its last curly brace, paste the following code:
static func createArcPathFromBottom( of rect: CGRect, arcHeight: CGFloat, startAngle: Angle, endAngle: Angle ) -> CGPath { // 1 let arcRect = CGRect( x: rect.origin.x, y: rect.origin.y + rect.height, width: rect.width, height: arcHeight) // 2 let arcRadius = (arcRect.height / 2) + pow(arcRect.width, 2) / (8 * arcRect.height) let arcCenter = CGPoint( x: arcRect.origin.x + arcRect.width / 2, y: arcRect.origin.y + arcRadius) let angle = acos(arcRect.width / (2 * arcRadius)) let startAngle = CGFloat(startAngle.toRadians()) + angle let endAngle = CGFloat(endAngle.toRadians()) - angle let path = CGMutablePath() // 3 path.addArc( center: arcCenter, radius: arcRadius, startAngle: startAngle, endAngle: endAngle, clockwise: false) path.addLine(to: CGPoint(x: rect.maxX, y: rect.minY)) path.addLine(to: CGPoint(x: rect.minX, y: rect.minY)) path.addLine(to: CGPoint(x: rect.minY, y: rect.maxY)) // 4 return path.copy()! }
There’s quite a bit going on here, so this is how it breaks down:
- This function takes a rectangle of the entire area and a float of how big the arc should be. Remember, the arc should be at the bottom of the rectangle. You calculate
arcRectgiven those two values.
- Then, you figure out the radius, center, start and end angles with the math discussed above.
- Next, you create the path. The path will consist of the arc and the lines around the edges of the rectangle above the arc.
- Finally, you return immutable copy of the path. You don’t want the path to be modified from outside the function.
CGContextextension,
createArcPathFromBottom(of:arcHeight:startAngle:endAngle:)returns a
CGPath. This is because the path will be reused many times. More on that later.
Now that you have a helper method to draw arcs in place, it’s time to replace your rectangular footer with your new curvy, arced one.
Open CustomFooter.swift and replace
draw(_:) with the following code:
override func draw(_ rect: CGRect) { let context = UIGraphicsGetCurrentContext()! let footerRect = CGRect( x: bounds.origin.x, y: bounds.origin.y, width: bounds.width, height: bounds.height) var arcRect = footerRect arcRect.size.height = 8 context.saveGState() let arcPath = CGContext.createArcPathFromBottom( of: arcRect, arcHeight: 4, startAngle: Angle(degrees: 180), endAngle: Angle(degrees: 360)) context.addPath(arcPath) context.clip() context.drawLinearGradient( rect: footerRect, startColor: .rwLightGray, endColor: .rwDarkGray) context.restoreGState() }
After the customary Core Graphics setup, you create a bounding box for the entire footer area and the area where you want the arc to be.
Then, you get the arc path by calling
createArcPathFromBottom(of:arcHeight:startAngle:endAngle:), the static method you just wrote. You can then add the path to your context and clip to that path.
All further drawing will be restricted to that path. Then, you can use
drawLinearGradient(rect:startColor:endColor:) found in Extensions.swift to draw a gradient from light gray to darker gray.
Again, build and run the app. If all works correctly, you should see the following screen:
Looks decent, but you need to polish it up a bit more.
Clipping, Paths and the Even-Odd Rule
In CustomFooter.swift add the following to the bottom of
draw(_:):
context.addRect(footerRect) context.addPath(arcPath) context.clip(using: .evenOdd) context.addPath(arcPath) context.setShadow( offset: CGSize(width: 0, height: 2), blur: 3, color: UIColor.rwShadow.cgColor) context.fillPath()
OK, there’s a new, and very important, concept going on here.
To draw a shadow, you enable shadow drawing, then fill a path. Core Graphics will then fill the path and also draw the appropriate shadow underneath.
But you’ve already filled the path with a gradient, so you don’t want to overwrite that area with a color.
Well, that sounds like a job for clipping! You can set up clipping so that Core Graphics will only draw in the portion outside the footer area. Then, you can tell it to fill the footer area and draw the shadow. Since its clipped, the footer area fill will be ignored, but the shadow will show through.
But you don’t have a path for this — the only path you have is for the footer area, not the outside.
You can easily get a path for the outside based on the inside through a neat ability of Core Graphics. You simply add more than one path to the context and then add clipping using a specific rule provided by Core Graphics.
When you add more than one path to a context, Core Graphics needs some way to determine which points should and shouldn’t be filled. For example, you could have a donut shape where the outside is filled but the inside is empty, or a donut-hole shape where the inside is filled but the outside is empty.
You can specify different algorithms to let Core Graphics know how to handle this. The algorithm you’ll use in this tutorial is EO, or even-odd.
In EO, for any given point, Core Graphics will draw a line from that point to the outside of the drawing area. If that line crosses an odd number of points, it will be filled. If it crosses an even number of points, it will not be filled.
Here’s a diagram showing this from the Quartz2D Programming Guide:
So, by calling the EO variant, you’re telling Core Graphics that, even though you’ve added two paths to the context, it should treat it as one path following the EO rule. So, the outside part, which is the entire footer rect, should be filled, but the inner part, which is the arc path, should not. You tell Core Graphics to clip to that path and only draw in the outside area.
Once you have the clipping area set up, you add the path for the arc, set up the shadow and fill the arc. Of course, since it’s clipped, nothing will actually be filled, but the shadow will still be drawn in the outside area!
Build and run the project and, if all goes well, you should now see a shadow underneath the footer:
Congratulations! You’ve created custom table view footers using Core Graphics!
Where to Go From Here?
You can download the completed version of the project using the Download Materials button at the top or the bottom of this tutorial.
By following this tutorial, you’ve learned how to create arcs and paths. Now you’ll be able to apply these concepts directly to your apps!
If you want to learn more about Core Graphics have a look at Quartz 2D Programming Guide.
In the meantime, if you have any questions or comments, please join the forum discussion below! | https://www.raywenderlich.com/349664-core-graphics-tutorial-arcs-and-paths | CC-MAIN-2022-33 | refinedweb | 2,246 | 66.44 |
How to Create an Enhanced for Loop in Java
To understand how to use Java’s enhanced for statement, consider how the laws of probability work. Your chance of winning one of the popular U.S. lottery jackpots is roughly 1 in 135,000,000.
If you sell your quarter-million dollar house and use all the money to buy lottery tickets, your chance of winning is still only 1 in 540. If you play every day of the month (selling a house each day), your chance of winning the jackpot is still less than 1 in 15.
To illustrate the idea of the enhanced for statement, you will see four symbols — a cherry, a lemon, a kumquat, and a rutabaga.
When you play this simplified slot machine, you can spin any one of over 60 combinations — cherry+cherry+kumquat, rutabaga+rutabaga+rutabaga, or whatever. The goal here is to list all possible combinations. But first, let’s take a look at another kind of loop. This code defines an enum type for a slot machine’s symbols and displays a list of the symbols.
import static java.lang.System.out; class ListSymbols { enum Symbol { cherry, lemon, kumquat, rutabaga } public static void main(String args[]) { for (Symbol leftReel : Symbol.values()) { out.println(leftReel); } } }
This code uses Java’s enhanced for loop. The word “enhanced” means “en-hanced compared with the loops in earlier versions of Java.” The enhanced for loop was introduced in Java version 5.0. If you run Java version 1.4.2 (or something like that), you can’t use an enhanced for loop.
Here’s the format of the enhanced for loop:
for (TypeName variableName : RangeOfValues) { Statements }
Here’s how the loop follows the format:
The word Symbol is the name of a type.
The int type describes values like –1, 0, 1, and 2. The boolean type describes the values true and false. And the Symbol type describes the values cherry, lemon, kumquat, and rutabaga.
The word leftReel is the name of a variable.
The loop in Listing 15-1 defines count to be an int variable. Similarly, the loop in Listing 15-5 defines leftReel to be a Symbol variable. So in theory, the variable leftReel can take on any of the four Symbol values.
The expression Symbol.values() stands for the four values in the code.
To quote myself in the previous bullet, “in theory, the variable leftReel can take on any of the four Symbol values.” Well, the RangeOfValues part of the for statement turns theory into practice. This third item inside the parentheses says, “Have as many loop iterations as there are Symbol values, and have the leftReel variable take on a different Symbol value during each of the loop’s iterations.”
So the loop undergoes four iterations — an iteration in which leftReel has value cherry, another iteration in which leftReel has value lemon, a third iteration in which leftReel has value kumquat, and a fourth iteration in which leftReel has value rutabaga. During each iteration, the program prints the leftReel variable’s value.
In general, a someEnumTypeName.values() expression stands for the set of values that a particular enum type’s variable can have. For example, you can use the expression WhoWins.values() to refer to the home, visitor, and neither values.
The difference between a type’s name (like Symbol) and the type’s values (as in Symbol.values()) is really subtle. Fortunately, you don’t have to worry about the difference. As a beginning programmer, you can just use the .values() suffix in an enhanced loop’s RangeOfValues part. | https://www.dummies.com/programming/java/how-to-create-an-enhanced-for-loop-in-java/ | CC-MAIN-2019-47 | refinedweb | 601 | 66.03 |
Link Previewer for iOS, macOS, watchOS and tvOS
It makes a preview from an URL, grabbing all the information such as title, relevant texts and images.
Index
- Visual Examples
- Requirements and Details
- Installation
- Usage
- Flow
- Important
- Tips
- Information and Contact
- Related Projects
- License
Visual Examples
Requirements and Details
- iOS 8.0+ / macOS 10.11+ / tvOS 9.0+ / watchOS 2.0+
- Xcode 8.0+
- Built with Swift 3
Installation
CocoaPods
To use SwiftLinkPreview as a pod package just add the following in your Podfile file.
source '' platform :ios, '9.0' target 'Your Target Name' do use_frameworks! // ... pod 'SwiftLinkPreview', '~> 2.2.0' // ... end
Carthage
To use SwiftLinkPreview as a Carthage module package just add the following in your Cartfile file.
// ... github "LeonardoCardoso/SwiftLinkPreview" ~> 2.2.0 // ...
Swift Package Manager
To use SwiftLinkPreview as a Swift Package Manager package just add the following in your Package.swift file.
import PackageDescription let package = Package( name: "Your Target Name", dependencies: [ // ... .Package(url: "", "2.2.0") // ... ] )
Manually
You just need to drop all contents in
Sources folder, but .plist files, into Xcode project (make sure to enable "Copy items if needed" and "Create groups").
Usage
Instatiating
import SwiftLinkPreview // ... let slp = SwiftLinkPreview(session: URLSession = URLSession.shared, workQueue: DispatchQueue = SwiftLinkPreview.defaultWorkQueue, responseQueue: DispatchQueue = DispatchQueue.main, cache: Cache = DisabledCache.instance)
Requesting preview
slp.preview("Text containing URL", onSuccess: { result in print("(result)") }, onError: { error in print("(error)")})
result is a dictionary
[String: AnyObject] like:
[ "url": "original URL", // NSURL "finalUrl": "final ~unshortened~ URL.", // NSURL "canonicalUrl": "canonical URL", // NSURL "title": "title", // String "description": "page description or relevant text", // String "images": ["array of URLs of the images"], // String array "image": "main image", // String "icon": "favicon" // String ]
Cancelling a request
let cancelablePreview = slp.preview(..., onSuccess: ..., onError: ...) cancelablePreview.cancel()
Enabling and accessing cache
SLP has a built-in memory cache, so create your object as the following:
let slp = SwiftLinkPreview(cache: InMemoryCache())
To get the cached response:
if let cached = self.slp.cache.slp_getCachedResponse(url: String) { // Do whatever with the cached response } else { // Perform preview otherwise slp.preview(...) }
If you want to create your own cache, just implement this protocol and use it on the object initializer.
public protocol Cache { func slp_getCachedResponse(url: String) -> SwiftLinkPreview.Response? func slp_setCachedResponse(url: String, response: SwiftLinkPreview.Response?) }
FLOW
Important.
Tips
Not all websites will have their info brought, you can treat the info that your implementation gets as you like. But here are two tips about posting a preview:
- If some info is missing, you can offer the user to enter it. Take for example the description.
- If more than one image is fetched, you can offer the user the feature of picking one image.
Tests
Feel free to fork this repo and add URLs on SwiftLinkPreviewTests/URLs.swift to test URLs and help improving this lib. The more URLs the better the reliability.
Information and Contact
Developed by @LeonardoCardoso.
Contact me either by Twitter @leocardz or emailing me to [email protected].
Related Projects
License
The MIT License (MIT) Copyright (c) 2016 Leonardo Cardoso": "SwiftLinkPreview", "platforms": { "ios": "8.0", "osx": "10.10", "watchos": "2.0", "tvos": "9.0" }, "summary": "It makes a preview from an url, grabbing all the information such as title, relevant texts and images.", "requires_arc": true, "version": "2.2.0", "license": { "type": "MIT", "file": "LICENSE" }, "authors": { "Leonardo Cardoso": "[email protected]" }, "homepage": "", "source": { "git": "", "tag": "2.2.0" }, "source_files": "Sources/**/*.swift", "pushed_with_swift_version": "4.0" }
Sat, 06 Jan 2018 11:20:51 +0000 | https://tryexcept.com/articles/cocoapod/swiftlinkpreview | CC-MAIN-2018-13 | refinedweb | 566 | 60.61 |
Posted 09 Dec 2014
Link to this post
I'm trying to create a custom orthogonal router that acts much like a schematic capture program. If you look at the youtube video in the link below, starting at 4m28s you will see what I am trying to achieve.
1. I need a custom router to make right angles when I add connections. I have listed the code below to show what I have so far, which basically adds two points to the middle of the connection, but it does not handle complex routing situations where it needs to route around other shapes.
2. Also, I would like the connection to start on a mouse click (press+release) and start routing as I move my mouse, then finally completing the connection with another mouse click (press+release). Any thoughts on how to achieve these two items?
public class OrthogonalRouter : IRouter
{
public System.Collections.Generic.IList<
Point
> GetRoutePoints(IConnection connection, bool showLastLine)
List<
> pointList = new List<
>();
Point start = connection.StartPoint;
Point end = connection.EndPoint;
pointList.Add(new Point(start.X + (end.X - start.X) / 2, start.Y));
pointList.Add(new Point(start.X + (end.X - start.X) / 2, end.Y));
return pointList;
}
Posted 12 Dec 2014
Link to this post
this
.diagram.RoutingService.Router =
new
AStarRouter(
.diagram);
.diagram.RoutingService.FreeRouter =
Check out the Telerik Platform - the only platform that combines a rich set of UI tools with powerful cloud services to develop web, hybrid and native mobile apps.
Posted 12 Dec 2014
in reply to
Petar Mladenov
Link to this post
Posted 15 Dec 2014
Link to this post
Posted 15 Dec 2014
in reply to
Petar Mladenov
Link to this post
Posted 16 Dec 2014
Link to this post
Posted 16 Dec 2014
in reply to
Petar Mladenov
Link to this post
Posted 17 Dec 2014
Link to this post
public
override
ConnectionRoute FindExtendedRoute(IConnection connection)
if
(connection.Source !=
null
&& connection.Source.IsSelected)
connection.IsModified =
false
;
Posted 23 Dec 2014
in reply to
Petar Mladenov
Link to this post
if (connection.Target != null && connection.Target.IsSelected)
connection.IsModified = false;
Posted 23 Feb 2015
Link to this post
Posted 24 Feb 2015
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MainWindow()
DiagramConstants.RouterInflationValue = 10;
InitializeComponent();
AStarRouter(diagram);
Posted 25 Feb 2015
in reply to
Milena
Link to this post
Posted 15 Mar
Link to this post
Hello,
I have seen it work however when saving and reloading it ignored the changes made. How can we persist the changes?
Posted 20 Mar
Link to this post | https://www.telerik.com/forums/orthogonal-routing-service-10bb0662a995 | CC-MAIN-2018-51 | refinedweb | 419 | 52.09 |
When creating a REST Service without a WADL, it is often useful to be able to generate these documents anyway, so that validation is made possible, and code/documentation generation tools can be used. For this SoapUI automatic inference of WADL from the model you create in SoapUI, and also inference of XSD schemas from any incoming responses that can be converted to XML, such as XML, JSON and HTML.
This brief tutorial will walk you through the schema inference functions of SoapUI. We'll start out by creating a new project, naming it "Demo Project". We'll be creating a REST service, without an initial WADL file, so check the "Add REST Service" check mark:
1. Creating the project and service
As a starting point for the service, we have the following URL:
Check the "Extract Resource/Method" check box, and SoapUI will parse the URL, extracting the parameters.
Three parameters have been extracted, these are "appid", "query" and "output". We are presented with the choice to place these parameters in either the resource, or the method. For this example, let's place the "query" and "output" parameters in the method, leaving the "appid" parameter in the resource. All methods inherit the parameters from their parent resource, and child resources inherit from their parent resources. Where to place a particular parameter depends on how we wish to structure the service.
Once the resource is created, we are presented with creating a method. The parameters we decided to place in the method are now shown here. Let's change the name of the method and then go on.
2. Inferring an XSD schema
Now we have a request to work with. The request holds all the parameters defined in one of its ancestors. These parameters have been pre-populated using the default values. Clicking on the green arrow icon submits the request, and we can view the response XML.
The response view has a tab along the bottom that now reads "Schema (conflicts)". This is the inferred schema inspector. It has analyzed the XML response, and is telling us that there are conflicts between the current response and the previously inferred schema. This is as it should be, as no prior schema exists. Clicking on the tab opens the inspector, and allows us to resolve these conflicts. Clicking the "Resolve conflicts" button prompts us with the first conflict and a proposed action, to which we can either accept or decline. Since the response we got looks OK, let's click on "Yes to all" to allow the schema inferrer to automatically resolve all conflicts.
If we now click on the "Schemas" tab of the inferred schema inspector, we are shown the inferred schemas for this project. So far we can see one namespace, and the associated XSD schema for it. As this schema is based on only one response we can refine it by making some more requests. While doing so we should try to vary the responses so that they are as different as possible. For instance, we should issue an invalid request so that we can infer the schema for a fault, we should make a request for a query that returns an empty result set (which can be done by setting the query parameter to a random string of characters of sufficient length), etc. While doing this against a working server, we assume the responses will always be valid, so we can check the "Auto-Resolve" check box on the "Conflicts" tab. After a bit of testing, we now see that we have two namespaces listed in the "Schemas" tab. These are "urn:yahoo_srchmi" and "urn:yahoo:api", the latter containing the "Error" element definition.
3. Using Inferred Schemas
These inferred schemas can be used just like manually created ones. This means that you can use them in assertions to validate your responses. You can export them together with the generated WADL to distribute, or use with other code-generating tools. You can even use them to generate HTML documentation for your service directly out of SoapUI.
4. Schema for JSON content
Schema inference in SoapUI works for any content that can be converted into XML internally. That means any response that shows up in the XML view can have a schema. Let's try this now.
Change the "output" parameters value to "json". This causes the response given from the service to be formatted in JSON instead of XML. For this demonstration, make sure that the "Auto-Resolve" check box in the inferred schema inspector is checked. Issue the request. Once the response has been returned we can view it both in JSON format, and in XML format converted by SoapUI. This XML representation is different in structure from the one we got when specifying "xml" as the output type. If we view the inferred schema inspector we can now see a new XSD schema. This is an inferred schema for the JSON response converted to XML. With this it is possible to assert the content of JSON responses.
| http://www.soapui.org/REST-Testing/schema-inference.html | CC-MAIN-2013-48 | refinedweb | 843 | 71.24 |
Sh here in Jordan and try to stay here illegally,” he says. “We already have our own unemployment problems, especially among the younger generation.”
Al-Faisal’s group has come up with a technological solution, utilizing drones and voice recognition. “The voice is the key. Native Arabic speakers in West Bank and East Bank populations have noticeable differences in their use of voiceless sibilant fricatives.” He points to a quadcopter drone, its four propellers whirring as it hovers in place. “We have installed a high-quality audio system onto these drones, with a speaker and directional microphones. The drone is autonomous. It presents a verbal challenge to the suspect. When the suspect answers, digital signal processing computes the coefficient of palatalization. East Bank natives have a mean palatalization coefficient of 0.85. With West Bank natives it is only 0.59. If the coefficient is below the acceptable threshold, the drone immobilizes the suspect with nonlethal methods until the nearest patrol arrives.”
One of Al-Faisal’s students presses a button and the drone zooms up and off to the west, embarking on another pilot run. If Al-Faisal’s system, the SIBFRIC-2000, proves to be successful in these test runs, it is likely to be used on a larger scale — so that limited Jordanian resources can cover a wider area to patrol for illegal immigrants. “Two weeks ago we caught a group of eighteen illegals with SIBFRIC. Border Security would never have found them. It’s not like in America, where you can discriminate against people because they look different. East Bank, West Bank — we all look the same. We sound different. I am confident the program will work.”
But some residents of the region are skeptical. “My brother was hit by a drone stunner on one of these tests,” says a 25-year old bus driver, who did not want his name to be used for this story. “They said his voice was wrong. Our family has lived in Jordan for generations. We are proud citizens! How can you trust a machine?”
Al-Faisal declines to give out statistics on how many cases like this have occurred, citing national security concerns. “The problem is being overstated. Very few of these incidents have occurred, and in each case the suspect is unharmed. It does not take long for Border Security to verify citizenship once they arrive.”
Others say there are rumors of voice coaches in Nablus and Ramallah, helping desperate refugees to beat the system. Al-Faisal is undeterred. “Ha ha ha, this is nonsense. SIBFRIC has a perfect ear; it can hear the slightest nuances of speech. You cannot cheat the computer.”
When asked how many drones are in the pilot program, Al-Faisal demures. “More than five,” he says, “fewer than five hundred.” Al-Faisal hopes to ramp up the drone program starting in 2021.
Shame Old Shtory, Shame Old Shong and Dansh
Does this story sound familiar? It might. Here’s a similar one from several thousand years earlier: (King James Version)
This is the reputed biblical origin of the term shibboleth, which has come to mean any distinguishing cultural behavior that can be used to identify a particular group, not just a linguistic one. The Ephraimites couldn’t say SHHHH and it became a dead giveaway of their origin.
In this article, we’re going to talk about the shibboleth and several other diagnostic tests which have one of two outcomes — pass or fail, yes or no, positive or negative — and some of the implications of using such a test. And yes, this does impact embedded systems. We’re going to spend quite a bit of time looking at a specific example in mathematical terms. If you don’t like math, just skip it whenever it gets too “mathy”.
A quantitative shibboleth detector
So let’s say we did want to develop a technological test for separating out people who couldn’t say SHHH, and we had some miracle algorithm to evaluate a “palatalization coefficient” \( P_{SH} \) for voiceless sibilant fricatives. How would we pick the threshold?
Well, the first thing to do is try to model the system somehow. We took a similar approach in an earlier article on design margin, where our friend the Oracle computed probability distributions for boiler pressures. Let’s do the same here. Suppose the Palestinians (which we’ll call Group 1) have a \( P_{SH} \) which roughly follows a Gaussian distribution with mean μ = 0.59 and standard deviation σ = 0.06, and the Jordanians (which we’ll call Group 2) have a \( P_{SH} \) which is also a Gaussian distribution with a mean μ = 0.85 and a standard deviation σ = 0.03.
import numpy as np import matplotlib.pyplot as plt %matplotlib inline import scipy.stats from collections import namedtuple class Gaussian1D(namedtuple('Gaussian1D','mu sigma name id color')): """ Normal (Gaussian) distribution of one variable """ def pdf(self, x): """ probabiliy density function """ return scipy.stats.norm.pdf(x, self.mu, self.sigma) def cdf(self, x): """ cumulative distribution function """ return scipy.stats.norm.cdf(x, self.mu, self.sigma) d1 = Gaussian1D(0.59, 0.06, 'Group 1 (Palestinian)','P','red') d2 = Gaussian1D(0.85, 0.03, 'Group 2 (Jordanian)','J','blue') def show_binary_pdf(d1, d2, x, fig=None, xlabel=None): if fig is None: fig = plt.figure(figsize=(6,3)) ax=fig.add_subplot(1,1,1) for d in (d1,d2): ax.plot(x,d.pdf(x),label=d.name,color=d.color) ax.legend(loc='best',labelspacing=0,fontsize=11) if xlabel is not None: ax.set_xlabel(xlabel, fontsize=15) ax.set_ylabel('probability density') return ax show_binary_pdf(d1,d2,x=np.arange(0,1,0.001), xlabel='$P_{SH}$');
Hmm, we have a dilemma here. Both groups have a small possibility that the \( P_{SH} \) measurement is in the 0.75-0.8 range, and this makes it harder to distinguish. Suppose we decided to set the threshold at 0.75. What would be the probability of our conclusion being wrong?
for d in (d1,d2): print '%-25s %f' % (d.name, d.cdf(0.75))
Group 1 (Palestinian) 0.996170 Group 2 (Jordanian) 0.000429
Here the
cdf method calls the
scipy.stats.norm.cdf function to compute the cumulative distribution function, which is the probability that a given sample from the distribution will be less than a given amount. So there’s a 99.617% chance that Group 1’s \( P_{SH} < 0.75 \), and a 0.0429% chance that Group 2’s \( P_{SH} < 0.75 \). One out of every 261 samples from Group 1 will pass the test (though we were hoping for them to fail) — this is known as a false negative, because a condition that exists (\( P_{SH} < 0.75 \)) remains undetected. One out of every 2331 samples from Group 2 will fail the test (though we were hoping for them to pass) — this is known as a false positive, because a condition that does not exist (\( P_{SH} < 0.75 \)) is mistakenly detected.
The probabilities of false positive and false negative are dependent on the threshold:
for threshold in [0.72,0.73,0.74,0.75,0.76,0.77,0.78]: c = [d.cdf(threshold) for d in (d1,d2)] print("threshold=%.2f, Group 1 false negative=%7.5f%%, Group 2 false positive=%7.5f%%" % (threshold, 1-c[0], c[1])) threshold = np.arange(0.7,0.801,0.005) false_positive = d2.cdf(threshold) false_negative = 1-d1.cdf(threshold) figure = plt.figure() ax = figure.add_subplot(1,1,1) ax.semilogy(threshold, false_positive, label='false positive', color='red') ax.semilogy(threshold, false_negative, label='false negative', color='blue') ax.set_ylabel('Probability') ax.set_xlabel('Threshold $P_{SH}$') ax.legend(labelspacing=0,loc='lower right') ax.grid(True) ax.set_xlim(0.7,0.8);
threshold=0.72, Group 1 false negative=0.01513%, Group 2 false positive=0.00001% threshold=0.73, Group 1 false negative=0.00982%, Group 2 false positive=0.00003% threshold=0.74, Group 1 false negative=0.00621%, Group 2 false positive=0.00012% threshold=0.75, Group 1 false negative=0.00383%, Group 2 false positive=0.00043% threshold=0.76, Group 1 false negative=0.00230%, Group 2 false positive=0.00135% threshold=0.77, Group 1 false negative=0.00135%, Group 2 false positive=0.00383% threshold=0.78, Group 1 false negative=0.00077%, Group 2 false positive=0.00982%
If we want a lower probability of false positives (fewer Jordanians detained for failing the test) we can do so by lowering the threshold, but at the expense of raising the probability of false negatives (more Palestinians unexpectedly passing the test and not detained), and vice-versa.
Factors used in choosing a threshold
There is a whole science around binary-outcome tests, primarily in the medical industry, involving sensivity and specificity, and it’s not just a matter of probability distributions. There are two other aspects that make a huge difference in determining a good test threshold:
- base rate — the probability of the condition actually being true, sometimes referred as prevalence in medical diagnosis
- the consequences of false positives and false negatives
Both of these are important because they affect our interpretation of false positive and false negative probabilities.
Base rate
The probabilities we calculated above are conditional probabilities — in our example, we calculated the probability that a person known to be from the Palestinian population passed the SIBFRIC test, and the probability that a person known to be from the Jordanian population failed the SIBFRIC tests.
It’s also important to consider the joint probability distribution — suppose that we are trying to detect a very uncommon condition. In this case the false positive rate will be amplified relative to the false negative rate. Let’s say we have some condition C that has a base rate of 0.001, or one in a thousand, and there is a test with a false positive rate of 0.2% and a false negative rate of 5%. This sounds like a really bad test: we should balance the probabilities by lowering the false negative rate and allowing a higher false positive rate. The net incidence of false positives for C will be 0.999 × 0.002 = 0.001998, and the net incidence of false negatives will be 0.001 × 0.05 = 0.00005. If we had one million people we test for condition C:
- 1000 actually have condition C
- 950 people are correctly diagnosed has having C
- 50 people will remain undetected (false negatives)
- 999000 do not actually have condition C
- 997002 people are correctly diagnosed as not having C
- 1998 people are incorrectly diagnosed as having C (false positives)
The net false positive rate is much higher than the net false negative rate, and if we had a different test with a false positive rate of 0.1% and a false negative rate of 8%, this might actually be better, even though the conditional probabilities of false positives and false negatives look even more lopsided. This is known as the false positive paradox.
Consequences
Let’s continue with our hypothetical condition C with a base rate of 0.001, and the test that has a false positive rate of 0.2% and a false negative rate of 5%. And suppose that the consequences of false positives are unnecessary hospitalization and the consequences of false negatives are certain death:
- 997002 diagnosed as not having C → relief
- 1998 incorrectly diagnosed as having C → unnecessary hospitalization, financial cost, annoyance
- 950 correctly diagnosed as having C → treatment, relief
- 50 incorrectly diagnosed as not having C → death
If the test can be changed, we might want to reduce the false negative, even if it raises the net false positive rate higher. Would lowering 50 deaths per million to 10 deaths per million be worth it if it raises the false positive rate of unnecessary hospitalization from 1998 per million to, say, 5000 per million? 20000 per million?
Consequences can rarely be compared directly; more often we have an apples-to-oranges comparison like death vs. unnecessary hospitalization, or allowing criminals to be free vs. incarcerating the innocent. If we want to handle a tradeof quantitatively, we’d need to assign some kind of metric for the consequences, like assigning a value of \$10 million for an unnecessary death vs. \$10,000 for an unnecessary hospitalization — in such a case we can minimize the net expected loss over an entire population. Otherwise it becomes an ethical question. In jurisprudence there is the idea of Blackstone’s ratio: “It is better that ten guilty persons escape than that one innocent suffer.” But the post-2001 political climate in the United States seems to be that detaining the innocent is more desirable than allowing terrorists or illegal immigrants to remain at large. Mathematics alone won’t help us out of these quandaries.
Optimizing a threshold
OK, so suppose we have a situation that can be described completely in mathematical terms:
- \( A \): Population A can be measured with parameter \( x \) with probability density function \( f_A(x) \) and cumulative density function \( F_A(x) = \int\limits_{-\infty}^x f_A(u) \, du \)
- \( B \): Population B can be measured with parameter \( x \) with PDF \( f_B(x) \) and CDF \( F_B(x) = \int\limits_{-\infty}^x f_B(u) \, du \)
- All samples are either in \( A \) or \( B \):
- \( A \) and \( B \) are disjoint (\( A \cap B = \varnothing \))
- \( A \) and \( B \) are collectively exhaustive (\( A \cup B = \Omega \), where \( \Omega \) is the full sample space, so that \( P(A \ {\rm or}\ B) = 1 \))
- Some threshold \( x_0 \) is determined
- For any given sample \( s \) that is in either A or B (\( s \in A \) or \( s \in B \), respectively), parameter \( x_s \) is compared with \( x_0 \) to determine an estimated classification \( a \) or \( b \):
- \( a \): if \( x_s > x_0 \) then \( s \) is likely to be in population A
- \( b \): if \( x_s \le x_0 \) then \( s \) is likely to be in population B
- Probability of \( s \in A \) is \( p_A \)
- Probability of \( s \in B \) is \( p_B = 1-p_A \)
- Value of various outcomes:
- \( v_{Aa} \): \( s \in A, x_s > x_0 \), correctly classified in A
- \( v_{Ab} \): \( s \in A, x_s \le x_0 \), incorrectly classified in B
- \( v_{Ba} \): \( s \in B, x_s > x_0 \), incorrectly classified in A
- \( v_{Bb} \): \( s \in B, x_s \le x_0 \), correctly classified in B
The expected value over all outcomes is
$$\begin{aligned} E[v] &= v_{Aa}P(Aa)+v_{Ab}P(Ab) + v_{Ba}P(Ba) + v_{Bb}P(Bb)\cr &= v_{Aa}p_A P(a\ |\ A) \cr &+ v_{Ab}p_A P(b\ |\ A) \cr &+ v_{Ba}p_B P(a\ |\ B) \cr &+ v_{Bb}p_B P(b\ |\ B) \end{aligned}$$
These conditional probabilities \( P(a\ |\ A) \) (denoting the probability of the classification \( a \) given that the sample is in \( A \)) can be determined with the CDF functions; for example, if the sample is in A then \( P(a\ |\ A) = P(x > x_0\ |\ A) = 1 - P(x \le x_0) = 1 - F_A(x_0) \), and once we know that, then we have
$$\begin{aligned} E[v] &= v_{Aa}p_A (1-F_A(x_0)) \cr &+ v_{Ab}p_A F_A(x_0) \cr &+ v_{Ba}p_B (1-F_B(x_0)) \cr &+ v_{Bb}p_B F_B(x_0) \cr E[v] &= p_A \left(v_{Ab} + (v_{Aa}-v_{Ab})\left(1-F_A(x_0)\right)\right) \cr &+ p_B \left(v_{Bb} + (v_{Ba}-v_{Bb})\left(1-F_B(x_0)\right)\right) \end{aligned}$$
\( E[v] \) is actually a function of the threshold \( x_0 \), and we can locate its maximum value by determining points where its partial derivative \( {\partial E[v] \over \partial {x_0}} = 0: \)
$$0 = {\partial E[v] \over \partial {x_0}} = p_A(v_{Ab}-v_{Aa})f_A(x_0) + p_B(v_{Bb}-v_{Ba})f_B(x_0)$$
where the \( \rho \) are ratios for probability and for value tradeoffs:
$$\begin{aligned} \rho_p &= p_B/p_A \cr \rho_v &= -\frac{v_{Bb}-v_{Ba}}{v_{Ab}-v_{Aa}} \end{aligned}$$
One interesting thing about this equation is that since probabilities \( p_A \) and \( p_B \) and PDFs \( f_A \) and \( f_B \) are positive, this means that \( v_{Bb}-v_{Ba} \) and \( v_{Ab}-v_{Aa} \) must be opposite signs, otherwise… well, let’s see:
Case study: Embolary Pulmonism
Suppose we have an obscure medical condition; let’s call it an embolary pulmonism, or EP for short. This must be treated within 48 hours, or the patient can transition in minutes from seeming perfectly normal, to a condition in which a small portion of their lungs degrade rapidly, dissolve, and clog up blood vessels elsewhere in the body, leading to extreme discomfort and an almost certain death. Before this rapid decline, the only symptoms are a sore throat and achy eyes.
We’re developing an inexpensive diagnostic test \( T_1 \) (let’s suppose it costs \$1) where the patient looks into a machine and it takes a picture of the patient’s eyeballs and uses machine vision to come up with some metric \( x \) that can vary from 0 to 100. We need to pick a threshold \( x_0 \) such that if \( x > x_0 \) we diagnose the patient with EP.
Let’s consider some math that’s not quite realistic:
- condition A: patient has EP
- condition B: patient does not have EP
- incidence of EP in patients complaining of sore throats and achy eyes: \( p_A = \) 0.004% (40 per million)
- value of Aa (correct diagnosis of EP): \( v_{Aa}=- \) \$100000
- value of Ab (false negative, patient has EP, diagnosis of no EP): \( v_{Ab}=0 \)
- value of Ba (false positive, patient does not have EP, diagnosis of EP): \( v_{Ba}=- \)\$5000
- value of Bb (correct diagnosis of no EP): \( v_{Bb} = 0 \)
So we have \( v_{Ab}-v_{Aa} = \) \$100000 and \( v_{Bb}-v_{Ba} = \) \$5000, for a \( \rho_v = -0.05, \) which implies that we’re looking for a threshold \( x_0 \) where \( \frac{f_A(x_0)}{f_B(x_0)} = -0.05\frac{p_B}{p_A} \) is negative, and that never occurs with any real probability distributions. In fact, if we look carefully at the values \( v \), we’ll see that when we diagnose a patient with EP, it always has a higher cost: If we correctly diagnose them with EP, it costs \$100,000 to treat. If we incorrectly diagnose them with EP, it costs \$5,000, perhaps because we can run a lung biopsy and some other fancy test to determine that it’s not EP. Whereas if we give them a negative diagnosis, it doesn’t cost anything. This implies that we should always prefer to give patients a negative diagnosis. So we don’t even need to test them!
Patient: “Hi, Doc, I have achy eyes and a sore throat, do I have EP?”
Doctor: (looks at patient’s elbows studiously for a few seconds) “Nope!”
Patient: (relieved) “Okay, thanks!”
What’s wrong with this picture? Well, all the values look reasonable except for two things. First, we haven’t included the \$1 cost of the eyeball test… but that will affect all four outcomes, so let’s just state that the values \( v \) are in addition to the cost of the test. The more important issue is the false negative, the Ab case, where the patient is diagnosed incorrectly as not having EP, and it’s likely the patient will die. Perhaps the hospital’s insurance company has estimated a cost of \$10 million per case to cover wrongful death civil suits, in which case we should be using \( v _ {Ab} = -\$10^7 \). So here’s our revised description:
- condition A: patient has EP
- condition B: patient does not have EP
- incidence of EP in patients complaining of sore throats and achy eyes: \( p_A = \) 0.004% (40 per million)
- value of Aa (correct diagnosis of EP): \( v_{Aa}=- \) \$100000 (rationale: mean cost of treatment)
- value of Ab (false negative, patient has EP, diagnosis of no EP): \( v_{Ab}=-\$10^7 \) (rationale: mean cost of resulting liability due to high risk of death)
- value of Ba (false positive, patient does not have EP, diagnosis of EP): \( v_{Ba}=- \)\$5000 (rationale: mean cost of additional tests to confirm)
- value of Bb (correct diagnosis of no EP): \( v_{Bb} = 0 \) (rationale: no further treatment needed)
The equation for choosing \( x_0 \) then becomes
$$\begin{aligned} \rho_p &= p_B/p_A = 0.99996 / 0.00004 = 24999 \cr \rho_v &= -\frac{v_{Bb}-v_{Ba}}{v_{Ab}-v_{Aa}} = -5000 / {-9.9}\times 10^6 \approx 0.00050505 \cr {f_A(x_0) \over f_B(x_0)} &= \rho_p\rho_v \approx 12.6258. \end{aligned}$$
Now we need to know more about our test. Suppose that the results of the eye machine test have normal probability distributions with \( \mu=55, \sigma=5.3 \) for patients with EP and \( \mu=40, \sigma=5.9 \) for patients without EP.
x = np.arange(0,100,0.1) dpos = Gaussian1D(55, 5.3, 'A (EP-positive)','A','red') dneg = Gaussian1D(40, 5.9, 'B (EP-negative)','B','green') show_binary_pdf(dpos, dneg, x, xlabel = 'test result $x$');
Yuck. This doesn’t look like a very good test; there’s a lot of overlap between the probability distributions.
At any rate, suppose we pick a threshold \( x_0=47 \); what kind of false positive / false negative rates will we get, and what’s the expected overall value?
import IPython.core.display from IPython.display import display, HTML def analyze_binary(dneg, dpos, threshold): """ Returns confusion matrix """ pneg = dneg.cdf(threshold) ppos = dpos.cdf(threshold) return np.array([[pneg, 1-pneg], [ppos, 1-ppos]]) def show_binary_matrix(confusion_matrix, threshold, distributions, outcome_ids, ppos, vmatrix, special_format=None): if special_format is None: special_format = {} def cellinfo(c, p, v): # joint probability = c*p jp = c*p return (c, jp, jp*v) def rowcalc(i,confusion_row): """ write this for rows containing N elements, not just 2 """ p = ppos if (i == 1) else (1-ppos) return [cellinfo(c,p,vmatrix[i][j]) for j,c in enumerate(confusion_row)] Jfmtlist = special_format.get('J') cfmtlist = special_format.get('c') vfmtlist = special_format.get('v') try: if isinstance(vfmtlist, basestring): vfmt_general = vfmtlist else: vfmt_general = vfmtlist[0] except: vfmt_general = '%.3f' def rowfmt(row,dist): def get_format(fmt, icell, default): if fmt is None: return default if isinstance(fmt,basestring): return fmt return fmt[icell] or default def cellfmt(icell): Jfmt = get_format(Jfmtlist, icell, '%.7f') cfmt = get_format(cfmtlist, icell, '%.5f') vfmt = get_format(vfmtlist, icell, '%.3f') return '<td>'+cfmt+'<br>J='+Jfmt+'<br>wv='+vfmt+'</td>' return '<th>'+dist.name+'</th>' + ''.join( (cellfmt(i) % cell) for i,cell in enumerate(row)) rows = [rowcalc(i,row) for i,row in enumerate(confusion_matrix)] vtot = sum(v for row in rows for c,J,v in row) if not isinstance (threshold, basestring): threshold = 'x_0 = %s' % threshold return HTML(('<p>Report for threshold \\(%s \\rightarrow E[v]=\\)' +vfmt_general+'</p>')%(threshold,vtot) +'<table><tr><td></td>'+ ''.join('<th>%s</th>' % id for id in outcome_ids) +'</tr>' +''.join('<tr>%s</tr>' % rowfmt(row,dist) for row,dist in zip(rows,distributions)) +'</table>') threshold = 47 C = analyze_binary(dneg, dpos, threshold) show_binary_matrix(C, threshold, [dneg, dpos], 'ba', 40e-6,[[0,-5000],[-1e7, -1e5]], special_format={'v':'$%.2f'})
Report for threshold \(x_0 = 47 \rightarrow E[v]=\)$-618.57
Here we’ve shown a modified confusion matrix showing for each of the four outcomes the following quantities:
- Conditional probability of each outcome: \( \begin{bmatrix}P(b\ |\ B) & P(a\ |\ B) \cr P(b\ |\ A) & P(a\ |\ A)\end{bmatrix} \) — read each entry like \( P(a\ |\ B) \) as “the probability of \( a \), given that \( B \) is true”, so that the numbers in each row add up to 1
- J: Joint probability of the outcome: \( \begin{bmatrix}P(Bb) & P(Ba) \cr P(Ab) & P(Aa)\end{bmatrix} \) — read each entry like \( P(Ba) \) as “The probability that \( B \) and \( a \) are true”, so that the numbers in the entire matrix add up to 1
- wv: Weighted contribution to expected value = joint probability of the outcome × its value
For example, if the patient does not have EP, there’s about an 88.2% chance that they will be diagnosed correctly and an 11.8% chance that the test will produce a false positive. If the patient does have EP, there’s about a 6.6% chance the test will produce a false negative, and a 93.4% chance the test will correctly diagnose that they have EP.
The really interesting thing here is the contribution to expected value. Remember, the false negative (Ab) is really bad, since it has a value of \$10 million, but it’s also very rare because of the low incidence of EP and the fact that condtional probability of a false negative is only 6.6%. Whereas the major contribution to expected value comes from the false positive case (Ba) that occurs in almost 11.8% of the population.
We should be able to use a higher threshold to reduce the expected cost over the population:
for threshold in [50, 55]: C = analyze_binary(dneg, dpos, threshold) display(show_binary_matrix(C, threshold, [dneg, dpos], 'ba', 40e-6,[[0,-5000],[-1e7, -1e5]], special_format={'v':'$%.2f'}))
Report for threshold \(x_0 = 50 \rightarrow E[v]=\)$-297.62
Report for threshold \(x_0 = 55 \rightarrow E[v]=\)$-229.52
The optimal threshold should probably be somewhere between \( x_0=50 \) and \( x_0=55 \), since in one case the contributions to expected value is mostly from the false positive case, and in the other from the false negative case. If we have a good threshold, these contributions are around the same order of magnitude from the false positive and false negative cases. (They won’t necessarily be equal, though.)
To compute this threshold we are looking for
$$\rho = {f_A(x_0) \over f_B(x_0)} = \rho_p\rho_v \approx 12.6258.$$
We can either solve it using numerical methods, or try to solve analytically using the normal distribution probability density
$$f(x) = \frac{1}{\sigma\sqrt{2\pi}}e^{-(x-\mu)^2/2\sigma^2}$$
which gives us
$$\frac{1}{\sigma_A}e^{-(x_0-\mu_A)^2/2\sigma_A{}^2} = \frac{1}{\sigma_B}\rho e^{-(x_0-\mu_B)^2/2\sigma_B{}^2}$$
and taking logs, we get
$$-\ln\sigma_A-(x_0-\mu_A)^2/2\sigma_A{}^2 = \ln\rho -\ln\sigma_B-(x_0-\mu_B)^2/2\sigma_B{}^2$$
If we set \( u = x_0 - \mu_A \) and \( \Delta = \mu_B - \mu_A \) then we get
$$-u^2/2\sigma_A{}^2 = \ln\rho\frac{\sigma_A}{\sigma_B} -(u-\Delta)^2/2\sigma_B{}^2$$
$$-\sigma_B{}^2u^2 = 2\sigma_A{}^2\sigma_B{}^2\left(\ln\rho\frac{\sigma_A}{\sigma_B} \right) -\sigma_A{}^2(u^2 - 2\Delta u + \Delta^2)$$
which simplifies to \( Au^2 + Bu + C = 0 \) with
$$\begin{aligned} A &= \sigma_B{}^2 - \sigma_A{}^2 \cr B &= 2\Delta\sigma_A{}^2 \cr C &= 2\sigma_A{}^2\sigma_B{}^2\left(\ln\rho\frac{\sigma_A}{\sigma_B}\right) - \Delta^2\sigma_A{}^2 \end{aligned}$$
We can solve this with the alternate form of the quadratic formula \( u = \frac{2C}{-B \pm \sqrt{B^2-4AC}} \) which can compute the root(s) even with \( A=0\ (\sigma_A = \sigma_B = \sigma) \), where it simplifies to \( u=-C/B=\frac{-\sigma^2 \ln \rho}{\mu_B - \mu_A} + \frac{\mu_B - \mu_A}{2} \) or \( x_0 = \frac{\mu_B + \mu_A}{2} - \frac{\sigma^2 \ln \rho}{\mu_B - \mu_A} \).
def find_threshold(dneg, dpos, ppos, vmatrix): num = -(1-ppos)*(vmatrix[0][0]-vmatrix[0][1]) den = ppos*(vmatrix[1][0]-vmatrix[1][1]) rho = num/den A = dneg.sigma**2 - dpos.sigma**2 ofs = dpos.mu delta = dneg.mu - dpos.mu B = 2.0*delta*dpos.sigma**2 C = (2.0 * dneg.sigma**2 * dpos.sigma**2 * np.log(rho*dpos.sigma/dneg.sigma) - delta**2 * dpos.sigma**2) if (A == 0): roots = [ofs-C/B] else: D = B*B-4*A*C roots = [ofs + 2*C/(-B-np.sqrt(D)), ofs + 2*C/(-B+np.sqrt(D))] # Calculate expected value, so that if we have more than one root, # the caller can determine which is better pneg = 1-ppos results = [] for i,root in enumerate(roots): cneg = dneg.cdf(root) cpos = dpos.cdf(root) Ev = (cneg*pneg*vmatrix[0][0] +(1-cneg)*pneg*vmatrix[0][1] +cpos*ppos*vmatrix[1][0] +(1-cpos)*ppos*vmatrix[1][1]) results.append((root,Ev)) return results find_threshold(dneg, dpos, 40e-6, [[0,-5000],[-1e7, -1e5]])
[(182.23914143860179, -400.00000000000006), (53.162644275683974, -212.51747111423805)]
threshold =53.1626 for x0 in [threshold, threshold-0.1, threshold+0.1]: C = analyze_binary(dneg, dpos, x0) display(show_binary_matrix(C, x0, [dneg, dpos], 'ba', 40e-6,[[0,-5000],[-1e7, -1e5]], special_format={'v':'$%.2f'}))
Report for threshold \(x_0 = 53.1626 \rightarrow E[v]=\)$-212.52
Report for threshold \(x_0 = 53.0626 \rightarrow E[v]=\)$-212.58
Report for threshold \(x_0 = 53.2626 \rightarrow E[v]=\)$-212.58
So it looks like we’ve found the threshold \( x_0 = 53.0626 \) to maximize expected value of all possible outcomes at \$-212.52. The vast majority (98.72%) of people taking the test don’t incur any cost or trouble beyond that of the test itself.
Still, it’s somewhat unsatisfying to have such a high false negative rate: over 36% of patients who are EP-positive are undetected by our test, and are likely to die. To put this into perspective, consider a million patients who take this test. The expected number of them for each outcome are
- 12842 will be diagnosed with EP but are actually EP-negative (false positive) and require \$5000 in tests to confirm
- 15 will be EP-positive but will not be diagnosed with EP (false negative) and likely to die
- 25 will be EP-positive and correctly diagnosed and incur \$100,000 in treatment
- the rest are EP-negative and correctly diagnosed.
That doesn’t seem fair to those 15 people, just to help reduce the false positive rate.
We could try skewing the test by assigning a value of \$100 million, rather than \$10 million, for the false negative case, because it’s really really bad:
find_threshold(dneg, dpos, 40e-6, [[0,-5000],[-1e8, -1e5]])
[(187.25596232479654, -4000.0000000000005), (48.145823389489138, -813.91495238472135)]
threshold = 48.1458 for x0 in [threshold, threshold-0.1, threshold+0.1]: C = analyze_binary(dneg, dpos, x0) display(show_binary_matrix(C, x0, [dneg, dpos], 'ba', 40e-6,[[0,-5000],[-1e8, -1e5]], special_format={'v':'$%.2f'}))
Report for threshold \(x_0 = 48.1458 \rightarrow E[v]=\)$-813.91
Report for threshold \(x_0 = 48.0458 \rightarrow E[v]=\)$-814.23
Report for threshold \(x_0 = 48.2458 \rightarrow E[v]=\)$-814.23
There, by moving the threshold downward by about 5 points, we’ve reduced the false negative rate to just under 10%, and the false positive rate is just over 8%. The expected value has nearly quadrupled, though, to \$-813.91, mostly because the false positive rate has increased, but also because the cost of a false negative is much higher.
Now, for every million people who take the test, we would expect
- around 83700 will have a false positive
- 36 will be correctly diagnosed with EP
- 4 will incorrectly remain undiagnosed and likely die.
Somehow that doesn’t sound very satisfying either. Can we do any better?
Idiot lights
Let’s put aside our dilemma of choosing a diagnosis threshold, for a few minutes, and talk about idiot lights. This term generally refers to indicator lights on automotive instrument panels, and apparently showed up in print around 1960. A July 1961 article by Phil McCafferty in Popular Science, called Let’s Bring Back the Missing Gauges, states the issue succinctly:
Car makers have you and me figured out for idiots — to the tune of about eight million dollars a year. This is the estimated amount that auto makers save by selling us little blink-out bulbs — known to fervent nonbelievers as “idiot lights” — on five million new cars instead of fitting them out with more meaningful gauges.
Not everything about blink-outs is bad. They do give a conspicuous warning when something is seriously amiss. But they don’t tell enough, or tell it soon enough to be wholly reliable. That car buyers aren’t happy is attested by the fact that gauge makers gleefully sell some quarter of a million accessory instruments a year to people who insist on knowing what’s going on under their hoods.
He goes on to say:
There’s little consolation in being told your engine has overheated after it’s done it. With those wonderful old-time gauges, a climbing needle gave you warning before you got into trouble.
The basic blink-out principle is contrary to all rules of safety. Blink-outs do not “fail safe.” The system operates on the assurance that all is well when the lights are off. If a bulb burns out while you’re traveling, you’ve lost your warning system.
Sure, most indicators remain on momentarily during starting, which makes it possible to check them for burnouts. But this has been known to have problems.
Consider the Midwestern husband who carefully lectured his young wife on the importance of watching gauges, then traded in the old car for a new blink-out model. Anxious to try it out, the wife fired it up the minute it arrived without waiting for her husband to come home. Panicked by three glaring lights, she assumed the worst, threw open the hood, and was met by the smell of new engine paint burning. Without hesitation, she popped off the cap and filled the crank-case to the brim—with water.
The big blink-out gripe is that the lights fail to tell the degree of what is taking place. Most oil-pressure blink-outs turn off at about 10 to 15 pounds’ pressure. Yet this is not nearly enough to lubricate an engine at 70 m.p.h.
The generator blink-out, unlike an ammeter, tells only whether or not the generator is producing current, not how much. You can be heading for a dead battery if you are using more current than the generator is producing. A battery can also be ruined by pouring an excessive charge into it, and over-production can kill a generator. Yet in all cases the generator is working, so the light is off.
The lights hide the secrets that a sinking, climbing, or fluctuating needle can reveal. Because of this, blink-outs are one of the greatest things that ever happened to a shady used-car dealer.
McCafferty seems to have been a bit of a zealot on this topic, publishing a November 1955 article in Popular Science, I Like the Gauges Detroit Left Out, though it doesn’t mention the term “idiot light”. The earliest use of “idiot light” in common media seems to be in the January 1960 issue of Popular Science, covering some automotive accessories like this volt-ammeter kit:
Interestingly enough, on the previous page is an article (TACHOMETER: You Can Assemble One Yourself with This \$14.95 Kit) showing a schematic and installation of a tachometer circuit that gets its input from one of the distributor terminals, and uses a PNP transistor to send a charge pulse to a capacitor and ammeter everytime the car’s distributor sends a high-voltage pulse to the spark plugs:
The earliest use of “idiot light” I could find in any publication is from a 1959 monograph on Standard Cells from the National Bureau of Standards which states
It is realized that the use of good-bad indicators must be approached with caution. Good-bad lights, often disparagingly referred to as idiot lights, are frequently resented by the technician because of the obvious implication. Furthermore, skilled technicians may feel that a good-bad indication does not give them enough information to support their intuitions. However, when all factors are weighed, good-bad indicators appear to best fit the requirements for an indication means that may be interpreted quickly and accurately by a wide variety of personnel whether trained or untrained.
Regardless of the term’s history, we’re stuck with these lights in many cases, and they’re a compromise between two principles:
- idiot lights are an effective and inexpensive method of catching the operator’s attention to one of many possible conditions that can occur, but they hide information by reducing a continuous value to a true/false indication
- a numeric result, shown by a dial-and-needle gauge or a numeric display, can show more useful information than an idiot light, but it is more expensive, doesn’t draw attention as easily as an idiot light, and it requires the operator to interpret the numeric value
¿Por qué no los dos?
If we don’t have an ultra-cost-sensitive system, why not have both? Computerized screens are very common these days, and it’s relatively easy to display both a PASS/FAIL or YES/NO indicator — for drawing attention to a possible problem — and a value that allows the operator to interpret the data.
Since 2008, new cars sold in the United States have been required to have a tire pressure monitoring system (TPMS). As a driver, I both love it and hate it. The TPMS is great for dealing with slow leaks before they become a problem. I carry a small electric tire pump that plugs into the 12V socket in my car, so if the TPMS light comes on, I can pull over, check the tire pressure, and pump up the one that has a leak to its normal range. I’ve had slow leaks that have lasted several weeks before they start getting worse. Or sometimes they’re just low pressure because it’s November or December and the temperature has decreased. What I don’t like is that there’s no numerical gauge. If my TPMS light comes on, I have no way to distinguish a slight decrease in tire pressure (25psi vs. the normal 30psi) vs. a dangerously low pressure (15psi), unless I stop and measure all four tires with a pressure gauge. I have no way to tell how quickly the tire pressure is decreasing, so I can decide whether to keep driving home and deal with it later, or whether to stop at the nearest possible service station. It would be great if my car had an information screen where I could read the tire pressure readings and decide what to do based on having that information.
As far as medical diagnostic tests go, using the extra information from a raw test score can be a more difficult decision, especially in cases where the chances and costs of both false positives and false negatives are high. In the EP example we looked at earlier, we had a 0-to-100 test with a threshold of somewhere in the 55-65 range. Allowing a doctor to use their judgment when interpreting this kind of a test might be a good thing, especially when the doctor can try to make use of other information. But as a patient, how am I to know? If I’m getting tested for EP and I have a 40 reading, my doctor can be very confident that I don’t have EP, whereas with a 75 reading, it’s a no-brainer to start treatment right away. But those numbers near the threshold are tricky.
Triage (¿Por qué no los tres?)
In medicine, the term triage refers to a process of rapid prioritization or categorization in order to determine which patients should be served first. The idea is to try to make the most difference, given limited resources — so patients who are sick or injured, but not in any immediate danger, may have to wait.
As an engineer, my colleagues and I use triage as a way to categorize issues so that we can focus only on the few that are most important. A couple of times a year we’ll go over the unresolved issues in our issue tracking database, to figure out which we’ll address in the near term. One of the things I’ve noticed is that our issues fall into three types:
- Issues which are obviously low priority — these are ones that we can look at in a few seconds and agree, “Oh, yeah, we don’t like that behavior but it’s just a minor annoyance and isn’t going to cause any real trouble.”
- Issues which are obviously high priority — these are ones that we can also look at in a few seconds and agree that we need to address them soon.
- Issues with uncertainty — we look at these and kind of sit and stare for a while, or have arguments within the group, about whether they’re important or not.
The ones in the last category take a lot of time, and slow this process down immensely. I would much rather come to a 30-second consensus of L/H/U (“low priority”/”high priority”/”uncertain”) and get through the whole list, then come back and go through the U issues one by one at a later date.
Let’s go back to our EP case, and use the results of our \$1 eyeball-photography test \( T_1 \), but instead of dividing our diagnosis into two outcomes, let’s divide it into three outcomes:
- Patients are diagnosed as EP-positive, with high confidence
- Patients for which the EP test is “ambivalent” and it is not possible to distinguish between EP-positive and EP-negative cases with high confidence
- Patients are diagnosed as EP-negative, with high confidence
We take the same actions in the EP-positive case (admit patient and begin treatment) and the EP-negative case (discharge patient) as before, but now we have this middle ground. What should we do? Well, we can use resources to evaluate the patient more carefully. Perhaps there’s some kind of blood test \( T_2 \), which costs \$100, but improves our ability to distinguish between EP-positive and EP-negative populations. It’s more expensive than the \$1 test, but much less expensive than the \$5000 run of tests we used in false positive cases in our example.
How can we evaluate test \( T_2 \)?
Bivariate normal distributions
Let’s say that \( T_2 \) also has a numeric result \( y \) from 0 to 100, and it has a Gaussian distribution as well, so that tests \( T_1 \) and \( T_2 \) return a pair of values \( (x,y) \) with a bivariate normal distribution, in particular both \( x \) and \( y \) can be described by their mean values \( \mu_x, \mu_y \), standard deviations \( \sigma_x, \sigma_y \) and correlation coefficient \( \rho \), so that the covariance matrix \( \operatorname{cov}(x,y) = \begin{bmatrix}S_{xx} & S_{xy} \cr S_{xy} & S_{yy}\end{bmatrix} \) can be calculated with \( S_{xx} = \sigma_x{}^2, S_{yy} = \sigma_y{}^2, S_{xy} = \rho\sigma_x\sigma_y. \)
When a patient has EP (condition A), the second-order statistics of \( (x,y) \) can be described as
- \( \mu_x = 55, \mu_y = 57 \)
- \( \sigma_x=5.3, \sigma_y=4.1 \)
- \( \rho = 0.91 \)
When a patient does not have EP (condition B), the second-order statistics of \( (x,y) \) can be described as
- \( \mu_x = 40, \mu_y = 36 \)
- \( \sigma_x=5.9, \sigma_y=5.2 \)
- \( \rho = 0.84 \)
The covariance matrix may be unfamiliar to you, but it’s not very complicated. (Still, if you don’t like the math, just skip to the graphs below.) Each of the entries of the covariance matrix is merely the expected value of the product of the variables in question after removing the mean, so with a pair of zero-mean random variables \( (x’,y’) \) with \( x’ = x - \mu_x, y’=y-\mu_y \), the covariance matrix is just \( \operatorname{cov}(x’,y’) = \begin{bmatrix}E[x’^2] & E[x’y’] \cr E[x’y’] & E[y’^2] \end{bmatrix} \)
In order to help visualize this, let’s graph the two conditions.
First of all, we need to know how to generate pseudorandom values with these distributions. If we generate two independent Gaussian random variables \( (u,v) \) with zero mean and unit standard deviation, then the covariance matrix is just \( \begin{bmatrix}1 & 0 \cr 0 & 1\end{bmatrix} \). We can create new random variables \( (x,y) \) as a linear combination of \( u \) and \( v \):
$$\begin{aligned}x &= a_1u + b_1v \cr y &= a_2u + b_2v \end{aligned}$$
In this case, \( \operatorname{cov}(x,y)=\begin{bmatrix}E[x^2] & E[xy] \cr E[xy] & E[y^2] \end{bmatrix} = \begin{bmatrix}a_1{}^2 + b_1{}^2 & a_1a_2 + b_1b_2 \cr a_1a_2 + b_1b_2 & a_2{}^2 + b_2{}^2 \end{bmatrix}. \) As an example for computing this, \( E[x^2] = E[(a_1u+b_1v)^2] = a_1{}^2E[u^2] + 2a_1b_1E[uv] + b_1{}^2E[v^2] = a_1{}^2 + b_1{}^2 \) since \( E[u^2]=E[v^2] = 1 \) and \( E[uv]=0 \).
We can choose values \( a_1, a_2, b_1, b_2 \) so that we achieve the desired covariance matrix:
$$\begin{aligned} a_1 &= \sigma_x \cos \theta_x \cr b_1 &= \sigma_x \sin \theta_x \cr a_2 &= \sigma_y \cos \theta_y \cr b_2 &= \sigma_y \sin \theta_y \cr \end{aligned}$$
which yields \( \operatorname{cov}(x,y) = \begin{bmatrix}\sigma_x^2 & \sigma_x\sigma_y\cos(\theta_x -\theta_y) \cr \sigma_x\sigma_y\cos(\theta_x -\theta_y) & \sigma_y^2 \end{bmatrix}, \) and therefore we can choose any \( \theta_x, \theta_y \) such that \( \cos(\theta_x -\theta_y) = \rho. \) In particular, we can always choose \( \theta_x = 0 \) and \( \theta_y = \cos^{-1}\rho \), so that
$$\begin{aligned} a_1 &= \sigma_x \cr b_1 &= 0 \cr a_2 &= \sigma_y \rho \cr b_2 &= \sigma_y \sqrt{1-\rho^2} \cr \end{aligned}$$
and therefore
$$\begin{aligned} x &= \mu_x + \sigma_x u \cr y &= \mu_y + \rho\sigma_y u + \sqrt{1-\rho^2}\sigma_y v \end{aligned}$$
is a possible method of constructing \( (x,y) \) from independent unit Gaussian random variables \( (u,v). \) (For the mean values, we just added them in at the end.)
OK, so let’s use this to generate samples from the two conditions A and B, and graph them:
from scipy.stats import chi2 import matplotlib.colors colorconv = matplotlib.colors.ColorConverter() Coordinate2D = namedtuple('Coordinate2D','x y') class Gaussian2D(namedtuple('Gaussian','mu_x mu_y sigma_x sigma_y rho name id color')): @property def mu(self): """ mean """ return Coordinate2D(self.mu_x, self.mu_y) def cov(self): """ covariance matrix """ crossterm = self.rho*self.sigma_x*self.sigma_y return np.array([[self.sigma_x**2, crossterm], [crossterm, self.sigma_y**2]]) def sample(self, N, r=np.random): """ generate N random samples """ u = r.randn(N) v = r.randn(N) return self._transform(u,v) def _transform(self, u, v): """ transform from IID (u,v) to (x,y) with this distribution """ rhoc = np.sqrt(1-self.rho**2) x = self.mu_x + self.sigma_x*u y = self.mu_y + self.sigma_y*self.rho*u + self.sigma_y*rhoc*v return x,y def uv2xy(self, u, v): return self._transform(u,v) def xy2uv(self, x, y): rhoc = np.sqrt(1-self.rho**2) u = (x-self.mu_x)/self.sigma_x v = ((y-self.mu_y) - self.sigma_y*self.rho*u)/rhoc/self.sigma_y return u,v def contour(self, c, npoint=360): """ generate elliptical contours enclosing a fraction c of the population (c can be a vector) R^2 is a chi-squared distribution with 2 degrees of freedom: """ r = np.sqrt(chi2.ppf(c,2)) if np.size(c) > 1 and len(np.shape(c)) == 1: r = np.atleast_2d(r).T th = np.arange(npoint)*2*np.pi/npoint return self._transform(r*np.cos(th), r*np.sin(th)) def pdf_exponent(self, x, y): xdelta = x - self.mu_x ydelta = y - self.mu_y return -0.5/(1-self.rho**2)*( xdelta**2/self.sigma_x**2 - 2.0*self.rho*xdelta*ydelta/self.sigma_x/self.sigma_y + ydelta**2/self.sigma_y**2 ) @property def pdf_scale(self): return 1.0/2/np.pi/np.sqrt(1-self.rho**2)/self.sigma_x/self.sigma_y def pdf(self, x, y): """ probability density function """ q = self.pdf_exponent(x,y) return self.pdf_scale * np.exp(q) def logpdf(self, x, y): return np.log(self.pdf_scale) + self.pdf_exponent(x,y) @property def logpdf_coefficients(self): """ returns a vector (a,b,c,d,e,f) such that log(pdf(x,y)) = ax^2 + bxy + cy^2 + dx + ey + f """ f0 = np.log(self.pdf_scale) r = -0.5/(1-self.rho**2) a = r/self.sigma_x**2 b = r*(-2.0*self.rho/self.sigma_x/self.sigma_y) c = r/self.sigma_y**2 d = -2.0*a*self.mu_x -b*self.mu_y e = -2.0*c*self.mu_y -b*self.mu_x f = f0 + a*self.mu_x**2 + c*self.mu_y**2 + b*self.mu_x*self.mu_y return np.array([a,b,c,d,e,f]) def project(self, axis): """ Returns a 1-D distribution on the specified axis """ if isinstance(axis, basestring): if axis == 'x': mu = self.mu_x sigma = self.sigma_x elif axis == 'y': mu = self.mu_y sigma = self.sigma_y else: raise ValueError('axis must be x or y') else: # assume linear combination of x,y a,b = axis mu = a*self.mu_x + b*self.mu_y sigma = np.sqrt((a*self.sigma_x)**2 +(b*self.sigma_y)**2 +2*a*b*self.rho*self.sigma_x*self.sigma_y) return Gaussian1D(mu,sigma,self.name,self.id,self.color) def slice(self, x=None, y=None): """ Returns information (w, mu, sigma) on the probability distribution with x or y constrained: w: probability density across the entire slice mu: mean value of the pdf within the slice sigma: standard deviation of the pdf within the slice """ if x is None and y is None: raise ValueError("At least one of x or y must be a value") rhoc = np.sqrt(1-self.rho**2) if y is None: w = scipy.stats.norm.pdf(x, self.mu_x, self.sigma_x) mu = self.mu_y + self.rho*self.sigma_y/self.sigma_x*(x-self.mu_x) sigma = self.sigma_y*rhoc else: # x is None w = scipy.stats.norm.pdf(y, self.mu_y, self.sigma_y) mu = self.mu_x + self.rho*self.sigma_x/self.sigma_y*(y-self.mu_y) sigma = self.sigma_x*rhoc return w, mu, sigma def slicefunc(self, which): rhoc = np.sqrt(1-self.rho**2) if which == 'x': sigma = self.sigma_y*rhoc a = self.rho*self.sigma_y/self.sigma_x def f(x): w = scipy.stats.norm.pdf(x, self.mu_x, self.sigma_x) mu = self.mu_y + a*(x-self.mu_x) return w,mu,sigma elif which == 'y': sigma = self.sigma_x*rhoc a = self.rho*self.sigma_x/self.sigma_y def f(y): w = scipy.stats.norm.pdf(y, self.mu_y, self.sigma_y) mu = self.mu_x + a*(y-self.mu_y) return w,mu,sigma else: raise ValueError("'which' must be x or y") return f DETERMINISTIC_SEED = 123 np.random.seed(DETERMINISTIC_SEED) N = 100000 distA = Gaussian2D(mu_x=55,mu_y=57,sigma_x=5.3,sigma_y=4.1,rho=0.91,name='A (EP-positive)',id='A',color='red') distB = Gaussian2D(mu_x=40,mu_y=36,sigma_x=5.9,sigma_y=5.2,rho=0.84,name='B (EP-negative)',id='B',color='#8888ff') xA,yA = distA.sample(N) xB,yB = distB.sample(N) fig=plt.figure() ax=fig.add_subplot(1,1,1) def scatter_samples(ax,xyd_list,contour_list=(),**kwargs): Kmute = 1 if not contour_list else 0.5 for x,y,dist in xyd_list: mutedcolor = colorconv.to_rgb(dist.color) mutedcolor = [c*Kmute+(1-Kmute) for c in mutedcolor] if not contour_list: kwargs['label']=dist.name ax.plot(x,y,'.',color=mutedcolor,alpha=0.8,markersize=0.5,**kwargs) for x,y,dist in xyd_list: # Now draw contours for certain probabilities th = np.arange(1200)/1200.0*2*np.pi u = np.cos(th) v = np.sin(th) first = True for p in contour_list: cx,cy = dist.contour(p) kwargs = {} if first: kwargs['label']=dist.name first = False ax.plot(cx,cy,color=dist.color,linewidth=0.5,**kwargs) ax.set_xlabel('x') ax.set_ylabel('y') ax.legend(loc='lower right',markerscale=10) ax.grid(True) title = 'Scatter sample plot' if contour_list: title += (', %s%% CDF ellipsoid contours shown' % (', '.join('%.0f' % (p*100) for p in contour_list))) ax.set_title(title, fontsize=10) scatter_samples(ax,[(xA,yA,distA), (xB,yB,distB)], [0.25,0.50,0.75,0.90,0.95,0.99]) for x,y,desc in [(xA, yA,'A'),(xB,yB,'B')]: print "Covariance matrix for case %s:" % desc C = np.cov(x,y) print C sx = np.sqrt(C[0,0]) sy = np.sqrt(C[1,1]) rho = C[0,1]/sx/sy print "sample sigma_x = %.3f" % sx print "sample sigma_y = %.3f" % sy print "sample rho = %.3f" % rho
Covariance matrix for case A: [[ 28.06613839 19.74199382] [ 19.74199382 16.76597717]] sample sigma_x = 5.298 sample sigma_y = 4.095 sample rho = 0.910 Covariance matrix for case B: [[ 34.6168817 25.69386711] [ 25.69386711 27.05651845]] sample sigma_x = 5.884 sample sigma_y = 5.202 sample rho = 0.840
It may seem strange, but having the results of two tests (\( x \) from test \( T_1 \) and \( y \) from test \( T_2 \)) gives more useful information than the result of each test considered on its own. We’ll come back to this idea a little bit later.
The more immediate question is: given the pair of results \( (x,y) \), how would we decide whether the patient has \( EP \) or not? With just test \( T_1 \) we could merely declare an EP-positive diagnosis if \( x > x_0 \) for some threshold \( x_0 \). With two variables, some kind of inequality is involved, but how do we decide?
Bayes’ Rule
We are greatly indebted to the various European heads of state and religion during much of the 18th century (the Age of Enlightenment) for merely leaving people alone. (OK, this wasn’t universally true, but many of the monarchies turned a blind eye towards intellectualism.) This lack of interference and oppression resulted in numerous mathematical and scientific discoveries, one of which was Bayes’ Rule, named after Thomas Bayes, a British clergyman and mathematician. Bayes’ Rule was published posthumously in An Essay towards solving a Problem in the Doctrine of Chances, and later inflicted on throngs of undergraduate students of probability and statistics.
The basic idea involves conditional probabilities and reminds me of the logical converse. As a hypothetical example, suppose we know that 95% of Dairy Queen customers are from the United States and that 45% of those US residents who visit Dairy Queen like peppermint ice cream, whereas 72% of non-US residents like peppermint ice cream. We are in line to get some ice cream, and we notice that the person in front of us orders peppermint ice cream. Can we make any prediction of the probability that this person is from the US?
Bayes’ Rule relates these two conditions. Let \( A \) represent the condition that a Dairy Queen customer is a US resident, and \( B \) represent that they like peppermint ice cream. Then \( P(A\ |\ B) = \frac{P(B\ |\ A)P(A)}{P(B)} \), which is really just an algebraic rearrangement of the expression of the joint probability that \( A \) and \( B \) are both true: \( P(AB) = P(A\ |\ B)P(B) = P(B\ |\ A)P(A) \). Applied to our Dairy Queen example, we have \( P(A) = 0.95 \) (95% of Dairy Queen customers are from the US) and \( P(B\ |\ A) = 0.45 \) (45% of customers like peppermint ice cream, given that they are from the US). But what is \( P(B) \), the probability that a Dairy Queen customer likes peppermint ice cream? Well, it’s the sum of the all the constituent joint probabilities where the customer likes peppermint ice cream. For example, \( P(AB) = P(B\ |\ A)P(A) = 0.45 \times 0.95 = 0.4275 \) is the joint probability that a Dairy Queen customer is from the US and likes peppermint ice cream, and \( P(\bar{A}B) = P(B\ |\ \bar{A})P(\bar{A}) = 0.72 \times 0.05 = 0.036 \) is the joint probability that a Dairy Queen customer is not from the US and likes peppermint ice cream. Then \( P(B) = P(AB) + P(\bar{A}B) = 0.4275 + 0.036 = 0.4635 \). (46.35% of all Dairy Queen customers like peppermint ice cream.) The final application of Bayes’ Rule tells us
$$P(A\ |\ B) = \frac{P(B\ |\ A)P(A)}{P(B)} = \frac{0.45 \times 0.95}{0.4635} \approx 0.9223$$
and therefore if we see someone order peppermint ice cream at Dairy Queen, there is a whopping 92.23% chance they are not from the US.
Let’s go back to our embolary pulmonism scenario where a person takes both tests \( T_1 \) and \( T_2 \), with results \( R = (x=45, y=52) \). Can we estimate the probability that this person has EP?
N = 500000 np.random.seed(DETERMINISTIC_SEED) xA,yA = distA.sample(N) xB,yB = distB.sample(N) fig=plt.figure() ax=fig.add_subplot(1,1,1) scatter_samples(ax,[(xA,yA,distA), (xB,yB,distB)]) ax.plot(45,52,'.k');
We certainly aren’t going to be able to find the answer exactly just from looking at this chart, but it looks like an almost certain case of A being true — that is, \( R: x=45, y=52 \) implies that the patient probably has EP. Let’s figure it out as
$$P(A\ |\ R) = \frac{P(R\ |\ A)P(A)}{P(R)}.$$
Remember we said earlier that the base rate, which is the probability of any given person presenting symptoms having EP before any testing, is \( P(A) = 40\times 10^{-6} \). (This is known as the a priori probability, whenever this Bayesian stuff gets involved.) The other two probabilities \( P(R\ |\ A) \) and \( P(R) \) are technically infinitesimal, because they are part of continuous probability distributions, but we can handwave and say that \( R \) is really the condition that the results are \( 45 \le x \le 45 + dx \) and \( 52 \le y \le 52+dy \) for some infinitesimal interval widths \( dx, dy \), in which case \( P(R\ |\ A) = p_A(R)\,dx\,dy \) and \( P(R) = P(R\ |\ A)P(A) + P(R\ |\ B)P(B) = p_A(R)P(A)\,dx\,dy + p_B(R)P(B)\,dx\,dy \) where \( p_A \) and \( p_B \) are the probability density functions. Substituting this all in we get
$$P(A\ |\ R) = \frac{p_A(R)P(A)}{p_A(R)P(A)+p_B(R)P(B)}$$
The form of the bivariate normal distribution is not too complicated, just a bit unwieldy:
$$p(x,y) = \frac{1}{2\pi\sqrt{1-\rho^2}\sigma_x\sigma_y}e^{q(x,y)}$$
with
$$q(x,y) = -\frac{1}{2(1-\rho^2)}\left(\frac{(x-\mu_x)^2}{\sigma_x{}^2}-2\rho\frac{(x-\mu_x)(y-\mu_y)}{\sigma_x\sigma_y}+\frac{(y-\mu_y)^2}{\sigma_y{}^2}\right)$$
and the rest is just number crunching:
x1=45 y1=52 PA_total = 40e-6 pA = distA.pdf(x1, y1) pB = distB.pdf(x1, y1) print "pA(%.1f,%.1f) = %.5g" % (x1,y1,pA) print "pB(%.1f,%.1f) = %.5g" % (x1,y1,pB) print ("Bayes' rule result: p(A | x=%.1f, y=%.1f) = %.5g" % (x1,y1,pA*PA_total/(pA*PA_total+pB*(1-PA_total))))
pA(45.0,52.0) = 0.0014503 pB(45.0,52.0) = 4.9983e-07 Bayes' rule result: p(A | x=45.0, y=52.0) = 0.104
Wow, that’s counterintuitive. This result value \( R \) lies much closer to the probability “cloud” of A = EP-positive than B = EP-negative, but Bayes’ Rule tells us there’s only about a 10.4% probability that a patient with test results \( (x=45, y=52) \) has EP. And it’s because of the very low incidence of EP.
There is something we can do to make reading the graph useful, and that’s to plot a parameter I’m going to call \( \lambda(x,y) \), which is the logarithm of the ratio of probability densities:
$$\lambda(x,y) = \ln \frac{p_A(x,y)}{p_B(x,y)} = \ln p_A(x,y) - \ln p_B(x,y)$$
Actually, we’ll plot \( \lambda_{10}(x,y) = \lambda(x,y) / \ln 10 = \log_{10} \frac{p_A(x,y)}{p_B(x,y)} \).
This parameter is useful because Bayes’ rule calculates
$$\begin{aligned} P(A\ |\ x,y) &= \frac{p_A(x,y) P_A} { p_A(x,y) P_A + p_B(x,y) P_B} \cr &= \frac{p_A(x,y)/p_B(x,y) P_A} {p_A(x,y)/p_B(x,y) P_A + P_B} \cr &= \frac{e^{\lambda(x,y)} P_A} {e^{\lambda(x,y)} P_A + P_B} \cr &= \frac{1}{1 + e^{-\lambda(x,y)}P_B / P_A} \end{aligned}$$
and for any desired \( P(A\ |\ x,y) \) we can figure out the equivalent value of \( \lambda(x,y) = - \ln \left(\frac{P_A}{P_B}((1/P(A\ |\ x,y) - 1)\right). \)
This means that for a fixed value of \( \lambda \), then \( P(A\ |\ \lambda) = \frac{1}{1 + e^{-\lambda}P_B / P_A}. \)
For bivariate Gaussian distributions, the \( \lambda \) parameter is also useful because it is a quadratic function of \( x \) and \( y \), so curves of constant \( \lambda \) are conic sections (lines, ellipses, hyperbolas, or parabolas).
def jcontourp(ax,x,y,z,levels,majorfunc,color=None,fmt=None, **kwargs): linewidths = [1 if majorfunc(l) else 0.4 for l in levels] cs = ax.contour(x,y,z,levels, linewidths=linewidths, linestyles='-', colors=color,**kwargs) labeled = [l for l in cs.levels if majorfunc(l)] ax.clabel(cs, labeled, inline=True, fmt='%s', fontsize=10) xv = np.arange(10,80.01,0.1) yv = np.arange(10,80.01,0.1) x,y = np.meshgrid(xv,yv) def lambda10(distA,distB,x,y): return (distA.logpdf(x, y)-distB.logpdf(x, y))/np.log(10) fig = plt.figure() ax = fig.add_subplot(1,1,1) scatter_samples(ax,[(xA,yA,distA), (xB,yB,distB)], zorder=-1) ax.plot(x1,y1,'.k') print "lambda10(x=%.1f,y=%.1f) = %.2f" % (x1,y1,lambda10(distA,distB,x1,y1)) levels = np.union1d(np.arange(-10,10), np.arange(-200,100,10)) def levelmajorfunc(level): if -10 <= level <= 10: return int(level) % 5 == 0 else: return int(level) % 25 == 0 jcontourp(ax,x,y,lambda10(distA,distB,x,y), levels, levelmajorfunc, color='black') ax.set_xlim(xv.min(), xv.max()+0.001) ax.set_ylim(yv.min(), yv.max()+0.001) ax.set_title('Scatter sample plot with contours = $\lambda_{10}$ values');
lambda10(x=45.0,y=52.0) = 3.46
We’ll pick one particular \( \lambda_{10} \) value as a threshold \( L_{10} = L/ \ln 10 \), and if \( \lambda_{10} > L_{10} \) then we’ll declare condition \( a \) (the patient is diagnosed as EP-positive), otherwise we’ll declare condition \( b \) (the patient is diagnosed as EP-negative). The best choice of \( L_{10} \) is the one that maximizes expected value.
Remember how we did this in the case with only the one test \( T_1 \) with result \( x \): we chose threshold \( x_0 \) based on the point where \( {\partial E \over \partial x_0} = 0 \); in other words, a change in diagnosis did not change the expected value at this point. We can do the same thing here:
$$0 = {\partial E[v] \over \partial {L}} = P(A\ |\ \lambda=L)(v_{Ab}-v_{Aa}) + P(B\ |\ \lambda=L)(v_{Bb}-v_{Ba})$$
With our earlier definitions
$$\rho_v = -\frac{v_{Bb}-v_{Ba}}{v_{Ab}-v_{Aa}}, \qquad \rho_p = P_B / P_A$$
then the equation for \( L \) becomes \( 0 = P(A\ |\ \lambda=L) - \rho_v P(B\ |\ \lambda=L) = P(A\ |\ \lambda=L) - \rho_v (1-P(A\ |\ \lambda=L)) \), which simplifies to
$$P(A\ |\ \lambda=L) = \frac{\rho_v}{\rho_v+1} = \frac{1}{1+1/\rho_v} .$$
But we already defined \( \lambda \) as the group of points \( (x,y) \) that have equal probability \( P(A\ |\ \lambda) = \frac{1}{1 + e^{-\lambda}P_B / P_A} = \frac{1}{1 + \rho_p e^{-\lambda}} \) so
$$\frac{1}{1+1/\rho_v} = \frac{1}{1 + \rho_p e^{-L}}$$
which occurs when \( L = \ln \rho_v \rho_p. \)
In our EP example,
$$\begin{aligned} \rho_p &= p_B/p_A = 0.99996 / 0.00004 = 24999 \cr \rho_v &= -\frac{v_{Bb}-v_{Ba}}{v_{Ab}-v_{Aa}} = -5000 / -9.9\times 10^6 \approx 0.00050505 \cr \rho_v\rho_p &\approx 12.6258 \cr L &= \ln \rho_v\rho_p \approx 2.5357 \cr L_{10} &= \log_{10}\rho_v\rho_p \approx 1.1013 \end{aligned}$$
and we can complete the analysis empirically by looking at the fraction of pseudorandomly-generated sample points where \( \lambda_{10} < L_{10} \); this is an example of Monte Carlo analysis.
class Quadratic1D(namedtuple('Quadratic1D','a b c')): """ Q(x) = a*x*x + b*x + c """ __slots__ = () @property def x0(self): return -self.b/(2.0*self.a) @property def q0(self): return self.c - self.a*self.x0**2 def __call__(self,x): return self.a*x*x + self.b*x + self.c def solve(self, q): D = self.b*self.b - 4*self.a*(self.c-q) sqrtD = np.sqrt(D) return np.array([-self.b-sqrtD, -self.b+sqrtD])/(2*self.a) class QuadraticLissajous(namedtuple('QuadraticLissajous','x0 y0 Rx Ry phi')): """ A parametric curve as a function of theta: x = x0 + Rx * cos(theta) y = y0 + Ry * sin(theta+phi) """ __slots__ = () def __call__(self, theta): return (self.x0 + self.Rx * np.cos(theta), self.y0 + self.Ry * np.sin(theta+self.phi)) class Quadratic2D(namedtuple('Quadratic2D','a b c d e f')): """ Bivariate quadratic function Q(x,y) = a*x*x + b*x*y + c*y*y + d*x + e*y + f = a*(x-x0)*(x-x0) + b*(x-x0)*(y-y0) + c*(y-y0)*(y-y0) + q0 = s*(u*u + v*v) + q0 where s = +/-1 (Warning: this implementation assumes convexity, that is, b*b < 4*a*c, so hyperboloids/paraboloids are not handled.) """ __slots__ = () @property def discriminant(self): return self.b**2 - 4*self.a*self.c @property def x0(self): return (2*self.c*self.d - self.b*self.e)/self.discriminant @property def y0(self): return (2*self.a*self.e - self.b*self.d)/self.discriminant @property def q0(self): x0 = self.x0 y0 = self.y0 return self.f - self.a*x0*x0 - self.b*x0*y0 - self.c*y0*y0 def _Kcomponents(self): s = 1 if self.a > 0 else -1 r = s*self.b/2.0/np.sqrt(self.a*self.c) rc = np.sqrt(1-r*r) Kux = rc*np.sqrt(self.a*s) Kvx = r*np.sqrt(self.a*s) Kvy = np.sqrt(self.c*s) return Kux, Kvx, Kvy @property def Kxy2uv(self): Kux, Kvx, Kvy = self._Kcomponents() return np.array([[Kux, 0],[Kvx, Kvy]]) @property def Kuv2xy(self): Kux, Kvx, Kvy = self._Kcomponents() return np.array([[1.0/Kux, 0],[-1.0*Kvx/Kux/Kvy, 1.0/Kvy]]) @property def transform_xy2uv(self): Kxy2uv = self.Kxy2uv x0 = self.x0 y0 = self.y0 def transform(x,y): return np.dot(Kxy2uv, [x-x0,y-y0]) return transform @property def transform_uv2xy(self): Kuv2xy = self.Kuv2xy x0 = self.x0 y0 = self.y0 def transform(u,v): return np.dot(Kuv2xy, [u,v]) + [[x0],[y0]] return transform def uv_radius(self, q): """ Returns R such that solutions (u,v) of Q(x,y) = q lie within the range [-R, R], or None if there are no solutions. """ s = 1 if self.a > 0 else -1 D = (q-self.q0)*s return np.sqrt(D) if D >= 0 else None def _xy_radius_helper(self, q, z): D = (self.q0 - q) * 4 * z / self.discriminant if D < 0: return None else: return np.sqrt(D) def x.c) def y.a) def lissajous(self, q): """ Returns a QuadraticLissajous with x0, y0, Rx, Ry, phi such that the solutions (x,y) of Q(x,y) = q can be written: x = x0 + Rx * cos(theta) y = y0 + Ry * sin(theta+phi) Rx and Ry and phi may each return None if no such solution exists. """ D = self.discriminant x0 = (2*self.c*self.d - self.b*self.e)/D y0 = (2*self.a*self.e - self.b*self.d)/D q0 = self.f - self.a*x0*x0 - self.b*x0*y0 - self.c*y0*y0 Dx = 4 * (q0-q) * self.c / D Rx = None if Dx < 0 else np.sqrt(Dx) Dy = 4 * (q0-q) * self.a / D Ry = None if Dy < 0 else np.sqrt(Dy) phi = None if D > 0 else np.arcsin(self.b / (2*np.sqrt(self.a*self.c))) return QuadraticLissajous(x0,y0,Rx,Ry,phi) def contour(self, q, npoints=360): """ Returns a pair of arrays x,y such that Q(x,y) = q """ s = 1 if self.a > 0 else -1 R = np.sqrt((q-self.q0)*s) th = np.arange(npoints)*2*np.pi/npoints u = R*np.cos(th) v = R*np.sin(th) return self.transform_uv2xy(u,v) def constrain(self, x=None, y=None): if x is None and y is None: return self if x is None: # return a function in x return Quadratic1D(self.a, self.d + y*self.b, self.f + y*self.e + y*y*self.c) if y is None: # return a function in y return Quadratic1D(self.c, self.e + x*self.b, self.f + x*self.d + x*x*self.a) return self(x,y) def __call__(self, x, y): return (self.a*x*x +self.b*x*y +self.c*y*y +self.d*x +self.e*y +self.f) def decide_limits(*args, **kwargs): s = kwargs.get('s', 6) xmin = None xmax = None for xbatch in args: xminb = min(xbatch) xmaxb = max(xbatch) mu = np.mean(xbatch) std = np.std(xbatch) xminb = min(mu-s*std, xminb) xmaxb = max(mu+s*std, xmaxb) if xmin is None: xmin = xminb xmax = xmaxb else: xmin = min(xmin,xminb) xmax = max(xmax,xmaxb) # Quantization q = kwargs.get('q') if q is not None: xmin = np.floor(xmin/q)*q xmax = np.ceil(xmax/q)*q return xmin, xmax def separation_plot(xydistA, xydistB, Q, L, ax=None, xlim=None, ylim=None): L10 = L/np.log(10) if ax is None: fig = plt.figure() ax = fig.add_subplot(1,1,1) xA,yA,distA = xydistA xB,yB,distB = xydistB scatter_samples(ax,[(xA,yA,distA), (xB,yB,distB)], zorder=-1) xc,yc = Q.contour(L) ax.plot(xc,yc, color='green', linewidth=1.5, dashes=[5,2], label = '$\\lambda_{10} = %.4f$' % L10) ax.legend(loc='lower right',markerscale=10, labelspacing=0,fontsize=12) if xlim is None: xlim = decide_limits(xA,xB,s=6,q=10) if ylim is None: ylim = decide_limits(yA,yB,s=6,q=10) xv = np.arange(xlim[0],xlim[1],0.1) yv = np.arange(ylim[0],ylim[1],0.1) x,y = np.meshgrid(xv,yv) jcontourp(ax,x,y,lambda10(distA,distB,x,y), levels, levelmajorfunc, color='black') ax.set_xlim(xlim) ax.set_ylim(ylim) ax.set_title('Scatter sample plot with contours = $\lambda_{10}$ values') def separation_report(xydistA, xydistB, Q, L): L10 = L/np.log(10) for x,y,dist in [xydistA, xydistB]: print "Separation of samples in %s by L10=%.4f" % (dist.id,L10) lam = Q(x,y) lam10 = lam/np.log(10) print " Range of lambda10: %.4f to %.4f" % (np.min(lam10), np.max(lam10)) n = np.size(lam) p = np.count_nonzero(lam < L) * 1.0 / n print " lambda10 < L10: %.5f" % p print " lambda10 >= L10: %.5f" % (1-p) L = np.log(5000 / 9.9e6 * 24999) C = distA.logpdf_coefficients - distB.logpdf_coefficients Q = Quadratic2D(*C) separation_plot((xA,yA,distA),(xB,yB,distB), Q, L) separation_report((xA,yA,distA),(xB,yB,distB), Q, L)
Or we can determine the results by numerical integration of probability density.
The math below isn’t difficult, just tedious; for each of the two Gaussian distributions for A and B, I selected a series of 5000 intervals (10001 x-axis points) from \( \mu_x-8\sigma_x \) to \( \mu_x + 8\sigma_x \), and used Simpson’s Rule to integrate the probability density \( f_x(x_i) \) at each point \( x_i \), given that
$$x \approx x_i \quad\Rightarrow\quad f_x(x) \approx f_x(x_i) = p_x(x_i) \left(F_{x_i}(y_{i2}) - F_{x_i}(y_{i1})\right)$$
where
- \( p_x(x_i) \) is the probability density that \( x=x_i \) with \( y \) unspecified
- \( F_{x_i}(y_0) \) is the 1-D cumulative distribution function, given \( x=x_i \), that \( y<y_0 \)
- \( y_{i1} \) and \( y_{i2} \) are either
- the two solutions of \( \lambda(x_i,y) = L \)
- or zero, if there are no solutions or one solution
and the sample points \( x_i \) are placed more closely together nearer to the extremes of the contour \( \lambda(x,y)=L \) to capture the suddenness of the change.
Anyway, here’s the result, which is nicely consistent with the Monte Carlo analysis:
def assert_ordered(*args, **kwargs): if len(args) < 2: return rthresh = kwargs.get('rthresh',1e-10) label = kwargs.get('label',None) label = '' if label is None else label+': ' xmin = args[0] xmax = args[-1] if len(args) == 2: # not very interesting case xthresh = rthresh*(xmax+xmin)/2.0 else: xthresh = rthresh*(xmax-xmin) xprev = xmin for x in args[1:]: assert x - xprev >= -xthresh, "%s%s > %s + %g" % (label,xprev,x,xthresh) xprev = x def arccos_sat(x): if x <= -1: return np.pi if x >= 1: return 0 return np.arccos(x) def simpsons_rule_points(xlist, bisect=True): """ Generator for Simpson's rule xlist: arbitrary points in increasing order bisect: whether or not to add bisection points returns a generator of weights w (if bisect=False) or tuples (w,x) (if bisect = True) such that the integral of f(x) dx over the list of points xlist is approximately equal to: sum(w*f(x) for w,x in simpsons_rule_points(xlist)) The values of x returned are x[i], (x[i]+x[i+1])/2, x[i+1] with relative weights dx/6, 4*dx/6, dx/6 for each interval [x[i], x[i+1]] """ xiter = iter(xlist) xprev = xiter.next() w2 = 0 x2 = None if bisect: for x2 in xiter: x0 = xprev dx = x2-x0 x1 = x0 + dx/2.0 xprev = x2 w6 = dx/6.0 w0 = w2 + w6 yield (w0, x0) w1 = 4*w6 yield (w1, x1) w2 = w6 if x2 is not None: yield (w2, x2) else: for x1 in xiter: x0 = xprev try: x2 = xiter.next() except StopIteration: raise ValueError("Must have an odd number of points") dx = x2-x0 xprev = x2 w6 = dx/6.0 w0 = w2 + w6 yield w0 w1 = 4*w6 yield w1 w2 = w6 if x2 is not None: yield w2 def estimate_separation_numerical(dist, Q, L, xmin, xmax, Nintervals=5000, return_pair=False, sampling_points=None): """ Numerical estimate of each row of confusion matrix using N integration intervals (each bisected to use Simpson's Rule) covering the interval [xmin,xmax]. dist: Gaussian2D distribution Q: Quadratic2D function Q(x,y) L: lambda threshold: diagnose as A when Q(x,y) > L, otherwise as B xmin: start x-coordinate xmax: end x-coordinate Nintervals: number of integration intervals Returns p, where p is the probability of Q(x,y) > L for that distribution. If return_pair is true, returns [p,q]; if [x1,x2] covers most of the distribution, then p+q should be close to 1. """ Qliss = Q.lissajous(L) xqr = Qliss.Rx xqmu = Qliss.x0 # Determine range of solutions: # no solutions if xqr is None, # otherwise Q(x,y) > L if x in Rx = [xqmu-xqr, xqmu+xqr] # # Cover the trivial cases first: if xqr is None: return (0,1) if return_pair else 0 if (xmax < xqmu - xqr) or (xmin > xqmu + xqr): # All solutions are more than Nsigma from the mean # isigma_left = (xqmu - xqr - dist.mu_x)/dist.sigma_x # isigma_right = (xqmu + xqr - dist.mu_x)/dist.sigma_x # print "sigma", isigma_left, isigma_right return (0,1) if return_pair else 0 # We want to cover the range xmin, xmax. # Increase coverage near the ends of the lambda threshold, # xqmu +/- xqr where the behavior changes more rapidly, # by using points at -cos(theta) within the solution space for Q(x,y)>L th1 = arccos_sat(-(xmin-xqmu)/xqr) th2 = arccos_sat(-(xmax-xqmu)/xqr) # print np.array([th1,th2])*180/np.pi, xmin, xqmu-np.cos(th1)*xqr, xqmu-np.cos(th2)*xqr, xmax, (xqmu-xqr, xqmu+xqr) assert_ordered(xmin, xqmu-np.cos(th1)*xqr, xqmu-np.cos(th2)*xqr, xmax) x_arc_coverage = xqr*(np.cos(th1)-np.cos(th2)) # length along x x_arc_length = xqr*(th2-th1) # length along arc x_total_length = (xmax-xmin) - x_arc_coverage + x_arc_length x1 = xqmu-xqr*np.cos(th1) x2 = x1 + x_arc_length n = (Nintervals*2) + 1 xlin = np.linspace(0,x_total_length, n) + xmin x = xlin[:] y = np.zeros((2,n)) # Points along arc: tol = 1e-10 i12 = (xlin >= x1 - tol) & (xlin <= x2 + tol) angles = th1 + (xlin[i12]-x1)/x_arc_length*(th2-th1) x[i12], y[0, i12] = Qliss(np.pi + angles) _, y[1, i12] = Qliss(np.pi - angles) y.sort(axis=0) x[xlin >= x2] += (x_arc_coverage-x_arc_length) fx = dist.slicefunc('x') p = 0 q = 0 for i,wdx in enumerate(simpsons_rule_points(x, bisect=False)): w, mu, sigma = fx(x[i]) y1 = y[0,i] y2 = y[1,i] cdf1 = scipy.stats.norm.cdf(y1, mu, sigma) cdf2 = scipy.stats.norm.cdf(y2, mu, sigma) deltacdf = cdf2-cdf1 p += wdx*w*deltacdf q += wdx*w*(1-deltacdf) return (p,q) if return_pair else p def compute_confusion_matrix(distA, distB, Q, L, Nintervals=5000, verbose=False): C = np.zeros((2,2)) for i,dist in enumerate([distA,distB]): Nsigma = 8 xmin = dist.mu_x - Nsigma*dist.sigma_x xmax = dist.mu_x + Nsigma*dist.sigma_x p,q = estimate_separation_numerical(dist, Q, L, xmin, xmax, Nintervals=Nintervals, return_pair=True) C[i,:] = [p,q] print "%s: p=%g, q=%g, p+q-1=%+g" % (dist.name, p,q,p+q-1) return C confusion_matrix = compute_confusion_matrix(distA, distB, Q, L, verbose=True) separation_report((xA,yA,distA),(xB,yB,distB), Q, L) value_matrix = np.array([[0,-5000],[-1e7, -1e5]]) - 100 # Same value matrix as the original one # (with vAb = $10 million) before but we add $100 cost for test T2 C = confusion_matrix[::-1,::-1] # flip the confusion matrix left-right and top-bottom for B first def gather_info(C,V,PA,**kwargs): info = dict(kwargs) C = np.array(C) V = np.array(V) info['C'] = C info['V'] = V info['J'] = C*[[1-PA],[PA]] return info display(show_binary_matrix(C, 'L_{10}=%.4f' % (L/np.log(10)), [distB, distA], 'ba', 40e-6,value_matrix, special_format={'v':'$%.2f'})) info27 = gather_info(C,value_matrix,40e-6,L=L)
A (EP-positive): p=0.982467, q=0.0175334, p+q-1=-8.90805e-09 B (EP-negative): p=0.00163396, q=0.998366, p+q-1=+1.97626e-07
Report for threshold \(L_{10}=1.1013 \rightarrow E[v]=\)$-119.11
There! Now we can check that we have a local maximum, by trying slightly lower and higher thresholds:
value_matrix = np.array([[0,-5000],[-1e7, -1e5]]) - 100 delta_L = 0.1*np.log(10) for Li in [L-delta_L, L+delta_L]: confusion_matrix = compute_confusion_matrix(distA, distB, Q, Li, verbose=True) separation_report((xA,yA,distA),(xB,yB,distB), Q, Li) # Same value matrix before but we add $100 cost for test T2 C = confusion_matrix[::-1,::-1] # flip the confusion matrix left-right and top-bottom for B first display(show_binary_matrix(C, 'L_{10}=%.4f' % (Li/np.log(10)), [distB, distA], 'ba', 40e-6,value_matrix, special_format={'v':'$%.2f'}))
A (EP-positive): p=0.984803, q=0.0151974, p+q-1=-8.85844e-09 B (EP-negative): p=0.0018415, q=0.998159, p+q-1=+2.55256e-07 Separation of samples in A by L10=1.0013 Range of lambda10: -3.4263 to 8.1128 lambda10 < L10: 0.01550 lambda10 >= L10: 0.98450 Separation of samples in B by L10=1.0013 Range of lambda10: -36.8975 to 4.0556 lambda10 < L10: 0.99819 lambda10 >= L10: 0.00181
Report for threshold \(L_{10}=1.0013 \rightarrow E[v]=\)$-119.23
A (EP-positive): p=0.979808, q=0.0201915, p+q-1=-9.01419e-09 B (EP-negative): p=0.00144637, q=0.998554, p+q-1=+2.1961e-08 Separation of samples in A by L10=1.2013 Range of lambda10: -3.4263 to 8.1128 lambda10 < L10: 0.02011 lambda10 >= L10: 0.97989 Separation of samples in B by L10=1.2013 Range of lambda10: -36.8975 to 4.0556 lambda10 < L10: 0.99850 lambda10 >= L10: 0.00150
Report for threshold \(L_{10}=1.2013 \rightarrow E[v]=\)$-119.23
Great! The sensitivity of threshold seems pretty flat; \( E[v] \) differs by about 12 cents if we change \( L_{10} = 1.1013 \) to \( L_{10} = 1.0013 \) or \( L_{10} = 1.2013 \). This gives us a little wiggle room in the end to shift costs between the false-negative and false-positive cases, without changing the overall expected cost very much.
Most notably, though, we’ve reduced the total cost by about \$93 by using the pair of tests \( T_1, T_2 \) compared to the test with just \( T_1 \). This is because we shift cost from the Ab (false negative for EP-positive) and Ba (false positive for EP-negative) cases to the Bb (correct for EP-negative) case — everyone has to pay \$100 more, but the chances of false positives and false negatives have been greatly reduced.
Don’t remember the statistics from the one-test case? Here they are again:
x0 = 53.1626 C = analyze_binary(dneg, dpos, x0) value_matrix_T1 = [[0,-5000],[-1e7, -1e5]] display(show_binary_matrix(C, x0, [dneg, dpos], 'ba', 40e-6,value_matrix_T1, special_format={'v':'$%.2f'})) info17 = gather_info(C,value_matrix_T1,40e-6,x0=x0)
Report for threshold \(x_0 = 53.1626 \rightarrow E[v]=\)$-212.52
And the equivalent cases for \( v_{Ab}= \)\$100 million:
Pa_total = 40e-6 x0 = 48.1458 C1 = analyze_binary(dneg, dpos, x0) value_matrix_T1 = np.array([[0,-5000],[-1e8, -1e5]]) display(show_binary_matrix(C1, x0, [dneg, dpos], 'ba', Pa_total, value_matrix_T1, special_format={'v':'$%.2f'})) info18 = gather_info(C1,value_matrix_T1,Pa_total,x0=x0) def compute_optimal_L(value_matrix,Pa_total): v = value_matrix return np.log(-(v[0,0]-v[0,1])/(v[1,0]-v[1,1])*(1-Pa_total)/Pa_total) value_matrix_T2 = value_matrix_T1 - 100 L = compute_optimal_L(value_matrix_T2, Pa_total) confusion_matrix = compute_confusion_matrix(distA, distB, Q, L, verbose=True) separation_report((xA,yA,distA),(xB,yB,distB), Q, L) # Same value matrix before but we add $100 cost for test T2 C2 = confusion_matrix[::-1,::-1] # flip the confusion matrix left-right and top-bottom for B first display(show_binary_matrix(C2, 'L_{10}=%.4f' % (L/np.log(10)), [distB, distA], 'ba', Pa_total,value_matrix_T2, special_format={'v':'$%.2f'})) separation_plot((xA,yA,distA),(xB,yB,distB), Q, L) info28 = gather_info(C2,value_matrix_T2,Pa_total,L=L)
Report for threshold \(x_0 = 48.1458 \rightarrow E[v]=\)$-813.91
A (EP-positive): p=0.996138, q=0.00386181, p+q-1=-8.37725e-09 B (EP-negative): p=0.00491854, q=0.995081, p+q-1=+4.32711e-08 Separation of samples in A by L10=0.0973 Range of lambda10: -3.4263 to 8.1128 lambda10 < L10: 0.00389 lambda10 >= L10: 0.99611 Separation of samples in B by L10=0.0973 Range of lambda10: -36.8975 to 4.0556 lambda10 < L10: 0.99514 lambda10 >= L10: 0.00486
Report for threshold \(L_{10}=0.0973 \rightarrow E[v]=\)$-144.02
Just as in the single-test case, by changing the test threshold in the case of using both tests \( T_1+T_2 \), we’ve traded a higher confidence in using the test results for patients who are EP-positive (Ab = false negative rate decreases from about 1.75% → 0.39%) for a lower confidence in the results for patients who are EP-negative (Ba = false positive rate increases from about 0.16% → 0.49%). This and the increased cost assessment for false negatives means that the expected cost increases from \$119.11 to \$144.02 — which is still much better than the expected value from the one-test cost of \$813.91.
In numeric terms, for every 10 million patients, with 400 expected EP-positive patients, we can expect
- 393 will be correctly diagnosed as EP-positive, and 7 will be misdiagnosed as EP-negative, with \( L_{10} = 1.1013 \)
- 398 will be correctly diagnosed as EP-positive, and 2 will be misdiagnosed as EP-negative, with \( L_{10} = 0.0973 \)
(The cynical reader may conclude that, since the addition of test \( T_2 \) results in a \$670 decrease in expected cost over all potential patients, then the hospital should be charging \$770 for test \( T_2 \), not \$100.)
It’s worth noting again that we can never have perfect tests; there is always some chance of the test being incorrect. The only way to eliminate all false negatives is to increase the chances of false positives to 1. Choice of thresholds is always a compromise.
Another thing to remember is that real situations are seldom characterized perfectly by normal (Gaussian) distributions; the probability of events way out in the tails is usually higher than Gaussian because of black-swan events.
Remember: Por qué no los tres?
We’re almost done. We’ve just shown that by having everyone take both tests, \( T_1 \) and \( T_2 \), we can maximize expected value (minimize expected cost) over all patients.
But that wasn’t the original idea. Originally we were going to do this:
- Have everyone take the \$1 test \( T_1 \), which results in a measurement \( x \)
- If \( x \ge x_{H} \), diagnose as EP-positive, with no need for test \( T_2 \)
- If \( x \le x_{L} \), diagnose as EP-negative, with no need for test \( T_2 \)
- If \( x_{L} < x < x_{H} \), we will have the patient take the \$100 test \( T_2 \), which results in a measurement \( y \)
- If \( \lambda_{10}(x,y) \ge L_{10} \), diagnose as EP-positive
- If \( \lambda_{10}(x,y) < L_{10} \), diagnose as EP-negative
where \( \lambda_{10}(x,y) = \lambda(x,y) / \ln 10 = \log_{10} \frac{p_A(x,y)}{p_B(x,y)}. \)
Now we just need to calculate thresholds \( x_H \) and \( x_L \). These are going to need to have very low false positive and false negative rates, and they’re there to catch the “obvious” cases without the need to charge for (and wait for) test \( T_2 \).
We have the same kind of calculation as before. Let’s consider \( x=x_H \). It should be chosen so that with the correct threshold, there’s no change in expected value if we change the threshold by a small amount. (\( \partial E[v] / \partial x_H = 0 \)). We can do this by finding \( x_H \) such that, within a narrow range \( x_H < x < x_H+\Delta x \), the expected value is equal for both alternatives, namely whether we have them take test \( T_2 \), or diagnose them as EP-positive without taking test \( T_2 \).
Essentially we are determining thresholds \( x_H \) and \( x_L \) that, at each threshold, make the additional value of information gained from test \( T_2 \) (as measured by a change in expected value) equal to the cost of test \( T_2 \).
Remember that the total probability of \( x_H < x < x_H+\Delta x \) is \( (P_A p_A(x_H) + (1-P_A)p_B(x_H))\Delta x \), broken down into
- \( P_A p_A(x_H) \Delta x \) for EP-positive patients (A)
- \( (1-P_A) p_B(x_H) \Delta x \) for EP-negative patients (B)
Expected value \( V_1 \) for diagnosing as EP-positive (a) without taking test \( T_2 \), divided by \( \Delta x \) so we don’t have to keep writing it:
$$V_1(x_H) = P_A v_{Aa}p_A(x_H) + (1-P_A) v_{Ba} p_B(x_H)$$
where \( p_A(x), p_B(x) \) are Gaussian PDFs of the results of test \( T_1 \).
Expected value \( V_2 \) taking test \( T_2 \), which has value \( v(T_2)=-\$100 \):
$$\begin{aligned} V_2(x_0) &= v(T_2) + P_A E[v\ |\ x_0, A]p_A(x_0) + P_B E[v\ |\ x_0, B]p_B(x_0) \cr &= v(T_2) + P_A \left(v_{Aa}P_{2a}(x_0\ |\ A) + v_{Ab}P_{2b}(x_0\ |\ A)\right) p_A(x_0) \cr &+ (1-P_A)\left(v_{Ba} P_{2a}(x_0\ |\ B) + v_{Bb}P_{2b}(x_0\ | B)\right)p_B(x_0) \end{aligned}$$
where \( P_{2A}(x_0), P_{2B}(x_0) \) are the conditional probabilities of declaring the patient as EP-positive or EP-negative based on tests \( T_1, T_2 \), given that \( x=x_0 \). This happens to be the numbers we used for numerical integration in the previous section (where we were making all patients take tests \( T_1,T_2 \)).
When we have an optimal choice of threshold \( x_H \), the expected values will be equal: \( V_1(x_H) = V_2(x_H) \), because there is no advantage. If \( V_1(x_H) < V_2(x_H) \), then we haven’t chosen a good threshold, and \( x_H \) should be lower; if \( V_1(x_H) > V_2(x_H) \) then \( x_H \) should be higher. (Example: suppose that \( x_H = 55, V_1(x_H) = -400, \) and \( V_2(x_H) = -250. \) The way we’ve defined \( x_H \) is that any result of test \( T_1 \) where \( x > x_H \), the value of \( x \) is high enough that we’re better off — in other words, the expected value is supposed to be higher — just declaring diagnosis \( a \) instead of spending the extra \$100 to get a result from test \( T_2 \), given its expected value. In mathematical terms, \( V_1(x) > V_2(x) \) as long as \( x > x_H \). But we can choose \( x = x_H + \delta \) with arbitrarily small \( \delta \), and in this case we have \( V_1(x_H + \delta) > V_2(x_H+\delta) \) which contradicts \( V_1(x_H) < V_2(x_H) \). Nitpicky mathematicians: this means that the expected values \( V_1(x_H) \) and \( V_2(x_H) \) as functions of threshold \( x_H \) are continuous there. The proof should be a trivial exercise for the reader, right?)
So we just need to find the right value of \( x_H \) such that \( V_1(x_H) = V_2(x_H) \).
Presumably there is a way to determine a closed-form solution here, but I won’t even bother; we’ll just evaluate it numerically.
We’ll also cover the case where we need to find \( x_L \), where we decide just to make a diagnosis \( b \) if \( x < x_L \) based on \( T_1 \) alone, and the resulting expected value is
$$V_1(x_L) = P_A v_{Ab}p_A(x_L) + (1-P_A) v_{Bb} p_B(x_L),$$
otherwise if \( x \ge x_L \), pay the \$100 to take test \( T_2 \) with expected value \( V_2(x_L) \).
Then we just need to find \( x_L \) such that \( V_1(x_L) = V_2(x_L). \)
Let’s get an idea of what these functions look like for our example.
def compute_value_densities(which_one, distA, distB, Pa_total, value_matrix, vT2, L): """ Returns a function to compute value densities V0, V1 """ fxA = distA.slicefunc('x') fxB = distB.slicefunc('x') vAa = value_matrix[1,1] vBa = value_matrix[0,1] vAb = value_matrix[1,0] vBb = value_matrix[0,0] if which_one == 'H': vA1 = vAa vB1 = vBa elif which_one == 'L': vA1 = vAb vB1 = vBb else: raise ValueError("which_one must be 'H' or 'L'") normcdf = scipy.stats.norm.cdf C = distA.logpdf_coefficients - distB.logpdf_coefficients Q = Quadratic2D(*C) Qliss = Q.lissajous(L) xqr = Qliss.Rx xqmu = Qliss.x0 # Find the center and radius of the contour lambda(x,y)=L def v1v2(x_0, verbose=False): wA, muA, sigmaA = fxA(x_0) wB, muB, sigmaB = fxB(x_0) # wA = probability density at x = x_0 given case A # wB = probability density at x = x_0 given case B # muA, sigmaA describe the pdf p(y | A,x=x0) # muB, sigmaB describe the pdf p(y | B,x=x0) if x_0 < xqmu - xqr or x_0 > xqmu + xqr: # x is extreme enough that we always diagnose as "b" P2Aa = 0 P2Ab = 1 P2Ba = 0 P2Bb = 1 else: # Here we need to find the y-value thresholds theta = np.arccos((x_0-xqmu)/xqr) x1,y1 = Qliss(theta) x2,y2 = Qliss(-theta) assert np.abs(x_0-x1) < 1e-10*xqr, (x_0,x1,x2) assert np.abs(x_0-x2) < 1e-10*xqr, (x_0,x1,x2) if y1 > y2: y1,y2 = y2,y1 assert np.abs(Q(x_0,y1) - L) < 1e-10 assert np.abs(Q(x_0,y2) - L) < 1e-10 # Diagnose as "a" if between the thresholds, otherwise "b" P2Aa = normcdf(y2, muA, sigmaA) - normcdf(y1, muA, sigmaA) P2Ab = 1-P2Aa P2Ba = normcdf(y2, muB, sigmaB) - normcdf(y1, muB, sigmaB) P2Bb = 1-P2Ba # expected value given the patient has results of both tests # over the full range of y vA2 = vAa*P2Aa+vAb*P2Ab # given A, x_0 vB2 = vBa*P2Ba+vBb*P2Bb # given B, x_0 # Bayes' rule for conditional probability of A and B given x_0 PA = (Pa_total*wA)/(Pa_total*wA + (1-Pa_total)*wB) PB = 1-PA v1 = PA*vA1 + PB*vB1 v2 = vT2 + PA*vA2 + PB*vB2 if verbose: print which_one, x_0 print "PA|x0=",PA print vAa,vAb,vBa,vBb print P2Aa, P2Ab, P2Ba, P2Bb print "T1 only", vA1,vB1 print "T1+T2 ", vA2,vB2 print "v1=%g v2=%g v2-v1=%g" % (v1,v2,v2-v1) return v1,v2 return v1v2 Pa_total = 40e-6 value_matrix_T1 = np.array([[0,-5000],[-1e7, -1e5]]) vT2 = -100 L = compute_optimal_L(value_matrix_T1 + vT2, Pa_total) distA2 = Gaussian2D(mu_x=63,mu_y=57,sigma_x=5.3,sigma_y=4.1,rho=0.91,name='A (EP-positive)',id='A',color='red') distB2 = Gaussian2D(mu_x=48,mu_y=36,sigma_x=5.9,sigma_y=5.2,rho=0.84,name='B (EP-negative)',id='B',color='#8888ff') print "For L10=%.4f:" % (L/np.log(10)) for which in 'HL': print "" v1v2 = compute_value_densities(which, distA, distB, Pa_total, value_matrix_T1, vT2, L) for x_0 in np.arange(25,100.1,5): v1,v2 = v1v2(x_0) print "x_%s=%.1f, V1=%.4g, V2=%.4g, V2-V1=%.4g" % (which, x_0,v1,v2,v2-v1)
For L10=1.1013: x_H=25.0, V1=-5000, V2=-100, V2-V1=4900 x_H=30.0, V1=-5000, V2=-100, V2-V1=4900 x_H=35.0, V1=-5000, V2=-100.5, V2-V1=4900 x_H=40.0, V1=-5000, V2=-104.2, V2-V1=4896 x_H=45.0, V1=-5001, V2=-122.2, V2-V1=4879 x_H=50.0, V1=-5011, V2=-183.7, V2-V1=4828 x_H=55.0, V1=-5107, V2=-394.5, V2-V1=4713 x_H=60.0, V1=-5840, V2=-1354, V2-V1=4487 x_H=65.0, V1=-1.033e+04, V2=-6326, V2-V1=4008 x_H=70.0, V1=-2.878e+04, V2=-2.588e+04, V2-V1=2902 x_H=75.0, V1=-6.315e+04, V2=-6.185e+04, V2-V1=1301 x_H=80.0, V1=-8.695e+04, V2=-8.661e+04, V2-V1=339.4 x_H=85.0, V1=-9.569e+04, V2=-9.567e+04, V2-V1=26.9 x_H=90.0, V1=-9.843e+04, V2=-9.849e+04, V2-V1=-59.82 x_H=95.0, V1=-9.933e+04, V2=-9.942e+04, V2-V1=-85.24 x_H=100.0, V1=-9.967e+04, V2=-9.976e+04, V2-V1=-93.59 x_L=25.0, V1=-0.001244, V2=-100, V2-V1=-100 x_L=30.0, V1=-0.0276, V2=-100, V2-V1=-100 x_L=35.0, V1=-0.5158, V2=-100.5, V2-V1=-99.95 x_L=40.0, V1=-8.115, V2=-104.2, V2-V1=-96.09 x_L=45.0, V1=-107.5, V2=-122.2, V2-V1=-14.63 x_L=50.0, V1=-1200, V2=-183.7, V2-V1=1016 x_L=55.0, V1=-1.126e+04, V2=-394.5, V2-V1=1.087e+04 x_L=60.0, V1=-8.846e+04, V2=-1354, V2-V1=8.711e+04 x_L=65.0, V1=-5.615e+05, V2=-6326, V2-V1=5.551e+05 x_L=70.0, V1=-2.503e+06, V2=-2.588e+04, V2-V1=2.477e+06 x_L=75.0, V1=-6.121e+06, V2=-6.185e+04, V2-V1=6.059e+06 x_L=80.0, V1=-8.627e+06, V2=-8.661e+04, V2-V1=8.54e+06 x_L=85.0, V1=-9.547e+06, V2=-9.567e+04, V2-V1=9.451e+06 x_L=90.0, V1=-9.835e+06, V2=-9.849e+04, V2-V1=9.736e+06 x_L=95.0, V1=-9.93e+06, V2=-9.942e+04, V2-V1=9.83e+06 x_L=100.0, V1=-9.965e+06, V2=-9.976e+04, V2-V1=9.865e+06
import matplotlib.gridspec def fVdistort(V): return -np.log(-np.array(V+ofs)) yticks0 =np.array([1,2,5]) yticks = -np.hstack([yticks0 * 10**k for k in xrange(-1,7)]) for which in 'HL': fig = plt.figure(figsize=(6,6)) gs = matplotlib.gridspec.GridSpec(2,1,height_ratios=[2,1],hspace=0.1) ax=fig.add_subplot(gs[0]) x = np.arange(20,100,0.2) fv1v2 = compute_value_densities(which, distA, distB, Pa_total, value_matrix_T1, vT2, L) v1v2 = np.array([fv1v2(xi) for xi in x]) vlim = np.array([max(-1e6,v1v2.min()*1.01), min(-10,v1v2.max()*0.99)]) f = fVdistort ax.plot(x,f(v1v2[:,0]),x_H') if which == 'H' else ('"b"', '<x_L'))) ax.plot(x,f(v1v2[:,1]),label='T1+T2') ax.set_yticks(f(yticks)) ax.set_yticklabels('%.0f' % y for y in yticks) ax.set_ylim(f(vlim)) ax.set_ylabel('$E[v]$',fontsize=12) ax.grid(True) ax.legend(labelspacing=0, fontsize=10, loc='lower left' if which=='H' else 'upper right') [label.set_visible(False) for label in ax.get_xticklabels()] ax2=fig.add_subplot(gs[1], sharex=ax) ax2.plot(x,v1v2[:,1]-v1v2[:,0]) ax2.set_ylim(-500,2000) ax2.grid(True) ax2.set_ylabel('$\\Delta E[v]$') ax2.set_xlabel('$x_%s$' % which, fontsize=12)
It looks like for this case (\( L_{10}=1.1013 \)), we should choose \( x_L \approx 45 \) and \( x_H \approx 86 \).
These edge cases where \( x < x_L \) or \( x > x_H \) don’t save a lot of money, at best just the \$100 \( T_2 \) test cost… so a not-quite-as-optimal but simpler case would be to always run both tests. Still, there’s a big difference between going to the doctor and paying \$1 rather than \$101… whereas once you’ve paid a \$100,000 hospital bill, what’s an extra \$100 among friends?
Between those thresholds, where test \( T_1 \) is kind of unhelpful, the benefit of running both tests is enormous: for EP-positive patients we can help minimize those pesky false negatives, saving hospitals millions in malpractice charges and helping those who would otherwise have grieving families; for EP-negative patients we can limit the false positives and save them the \$5000 and anguish of a stressful hospital stay.
Putting it all together
Now we can show our complete test protocol on one graph and one chart. Below the colored highlights show four regions:
- blue: \( b_1 \) — EP-negative diagnosis after taking test \( T_1 \) only, with \( x<x_L \)
- green: \( b_2 \) — EP-negative diagnosis after taking tests \( T_1, T_2 \), with \( x_L \le x \le x_H \) and \( \lambda_{10} < L_{10} \)
- yellow: \( a_2 \) — EP-positive diagnosis after taking tests \( T_1, T_2 \), with \( x_L \le x \le x_H \) and \( \lambda_{10} \ge L_{10} \)
- red: \( a_1 \) — EP-positive diagnosis after taking tests \( T_1 \) only, with \( x > x_H \)
import matplotlib.patches as patches import matplotlib.path import scipy.optimize Path = matplotlib.path.Path def show_complete_chart(xydistA, xydistB, Q, L, Pa_total, value_matrix_T1, vT2, return_info=False): fig = plt.figure() ax = fig.add_subplot(1,1,1) xlim = (0,100) ylim = (0,100) separation_plot(xydistA, xydistB, Q, L, ax=ax, xlim=xlim, ylim=ylim) ax.set_xticks(np.arange(0,101.0,10)) ax.set_yticks(np.arange(0,101.0,10)) # Solve for xL and xH _,_,distA = xydistA _,_,distB = xydistB v1v2 = [compute_value_densities(which, distA, distB, Pa_total, value_matrix_T1, vT2, L) for which in 'LH'] def fdelta(f): def g(x): y1,y2 = f(x) return y1-y2 return g xL = scipy.optimize.brentq(fdelta(v1v2[0]), 0, 100) xH = scipy.optimize.brentq(fdelta(v1v2[1]), 0, 100) # Show the full matrix of possibilities: # compute 2x4 confusion matrix C = [] for dist in [distB, distA]: distx = dist.project('x') pa2,pb2 = estimate_separation_numerical(dist, Q, L, xL, xH, Nintervals=2500, return_pair=True) row = [distx.cdf(xL), pb2, pa2, 1-distx.cdf(xH)] C.append(row) # compute 2x4 value matrix V = value_matrix_T1.repeat(2,axis=1) V[:,1:3] += vT2 display(show_binary_matrix(confusion_matrix=C, threshold='x_L=%.3f, x_H=%.3f, L_{10}=%.3f' %(xL,xH,L/np.log(10)), distributions=[distB,distA], outcome_ids=['b1','b2','a2','a1'], ppos=Pa_total, vmatrix=V, special_format={'v':'$%.2f', 'J':['%.8f','%.8f','%.8f','%.3g']})) # Highlight each of the areas x0,x1 = xlim y0,y1 = ylim # area b1: x < xL rect = patches.Rectangle((x0,y0),xL-x0,y1-y0,linewidth=0,edgecolor=None,facecolor='#8888ff',alpha=0.1) ax.add_patch(rect) # area a1: x > xH rect = patches.Rectangle((xH,y0),x1-xH,y1-y0,linewidth=0,edgecolor=None,facecolor='red',alpha=0.1) ax.add_patch(rect) for x in [xL,xH]: ax.plot([x,x],[y0,y1],color='gray') # area a2: lambda(x,y) > L xc,yc = Q.contour(L) ii = (xc > xL-10) & (xc < xH + 10) xc = xc[ii] yc = yc[ii] xc = np.maximum(xc,xL) xc = np.minimum(xc,xH) poly2a = patches.Polygon(np.vstack([xc,yc]).T, edgecolor=None, facecolor='yellow',alpha=0.5) ax.add_patch(poly2a) # area b2: lambda(x,y) < L xy = [] op = [] i = 0 for x,y in zip(xc,yc): i += 1 xy.append((x,y)) op.append(Path.MOVETO if i == 1 else Path.LINETO) xy.append((0,0)) op.append(Path.CLOSEPOLY) xy += [(xL,y0),(xL,y1),(xH,y1),(xH,y0),(0,0)] op += [Path.MOVETO, Path.LINETO, Path.LINETO, Path.LINETO, Path.CLOSEPOLY] patch2b = patches.PathPatch(Path(xy,op), edgecolor=None, facecolor='#00ff00',alpha=0.1) ax.add_patch(patch2b) # add labels style = {'fontsize': 28, 'ha':'center'} ax.text((x0+xL)/2,y0*0.3+y1*0.7,'$b_1$', **style) ax.text(xc.mean(), yc.mean(), '$a_2$', **style) a = 0.3 if yc.mean() > (x0+x1)/2 else 0.7 yb2 = a*y1 + (1-a)*y0 ax.text(xc.mean(), yb2, '$b_2$',**style) xa1 = (xH + x1) / 2 ya1 = max(30, min(90, Q.constrain(x=xa1).x0)) ax.text(xa1,ya1,'$a_1$',**style) if return_info: C = np.array(C) J = C * [[1-Pa_total],[Pa_total]] return dict(C=C,J=J,V=V,xL=xL,xH=xH,L=L) value_matrix_T1 = np.array([[0,-5000],[-1e7, -1e5]]) value_matrix_T2 = value_matrix_T1 - 100 L = compute_optimal_L(value_matrix_T2, Pa_total) info37 = show_complete_chart((xA,yA,distA),(xB,yB,distB), Q, L, Pa_total, value_matrix_T1, vT2, return_info=True)
Report for threshold \(x_L=45.287, x_H=85.992, L_{10}=1.101 \rightarrow E[v]=\)$-46.88
We can provide the same information but with the false negative cost (Ab = wrongly diagnosed EP-negative) at \$100 million:
value_matrix_T1 = np.array([[0,-5000],[-1e8, -1e5]]) value_matrix_T2 = value_matrix_T1 - 100 L = compute_optimal_L(value_matrix_T2, Pa_total) info38 = show_complete_chart((xA,yA,distA),(xB,yB,distB), Q, L, Pa_total, value_matrix_T1, vT2, return_info=True)
Report for threshold \(x_L=40.749, x_H=85.108, L_{10}=0.097 \rightarrow E[v]=\)$-99.60
Do we need test \( T_1 \)?
If adding test \( T_2 \) is so much better than test \( T_1 \) alone, why do we need test \( T_1 \) at all? What if we just gave everyone test \( T_2 \)?
y = np.arange(0,100,0.1) distA_T2 = distA.project('y') distB_T2 = distB.project('y') show_binary_pdf(distA_T2, distB_T2, y, xlabel = '$T_2$ test result $y$') for false_negative_cost in [10e6, 100e6]: value_matrix_T2 = np.array([[0,-5000],[-false_negative_cost, -1e5]]) - 100 threshold_info = find_threshold(distB_T2, distA_T2, Pa_total, value_matrix_T2) y0 = [yval for yval,_ in threshold_info if yval > 20 and yval < 80][0] C = analyze_binary(distB_T2, distA_T2, y0) print "False negative cost = $%.0fM" % (false_negative_cost/1e6) display(show_binary_matrix(C, 'y_0=%.2f' % y0, [distB_T2, distA_T2], 'ba', Pa_total, value_matrix_T2, special_format={'v':'$%.2f'})) info = gather_info(C,value_matrix_T2,Pa_total,y0=y0) if false_negative_cost == 10e6: info47 = info else: info48 = info
False negative cost = $10M
Report for threshold \(y_0=50.14 \rightarrow E[v]=\)$-139.03
False negative cost = $100M
Report for threshold \(y_0=47.73 \rightarrow E[v]=\)$-211.68
Hmm. That seems better than the \( T_1 \) test… but the confusion matrix doesn’t seem as good as using both tests.
d prime \( (d’) \): Are two tests are always better than one?
Why would determining a diagnosis based on both tests \( T_1 \) and \( T_2 \) be better than from either test alone?
Let’s graph the PDFs of three different measurements:
- \( x \) (the result of test \( T_1 \))
- \( y \) (the result of test \( T_2 \))
- \( u = -0.88x + 1.88y \) (a linear combination of the two measurements)
We’ll also calculate a metric for each of the three measurements,
$$d’ = \frac{\mu_A - \mu_B}{\sqrt{\frac{1}{2}(\sigma_A{}^2 + \sigma_B{}^2)}}$$
which is a measure of the “distinguishability” between two populations which each have normal distributions. Essentially it is a unitless “separation coefficient” that measures the distances between the means as a multiple of the “average” standard deviation. It is also invariant under scaling and translation — if we figure out the value of \( d’ \) for some measurement \( x \), then any derived measurement \( u = ax + c \) has the same value for \( d’ \) as long as \( a \ne 0 \).
(We haven’t talked about derived measurements like \( u \), but for a 2-D Gaussian distribution, if \( u=ax+by+c \) then:
$$\begin{aligned} \mu_u &= E[u] = aE[x]+bE[y] = a\mu_x + b\mu_y + c\cr \sigma_u{}^2 &= E[(u-\mu_u)^2] \cr &= E[a^2(x-\mu_x)^2 + 2ab(x-\mu_x)(y-\mu_y) + b^2(y-\mu_y)^2] \cr &= a^2E[(x-\mu_x)^2] + 2abE[(x-\mu_x)(y-\mu_y)] + b^2E[(y-\mu_y)^2] \cr &= a^2 \sigma_x{}^2 + 2ab\rho\sigma_x\sigma_y + b^2\sigma_y{}^2 \end{aligned}$$
or, alternatively using matrix notation, \( \sigma_u{}^2 = \mathrm{v}^T \mathrm{S} \mathrm{v} \) where \( \mathrm{v} = \begin{bmatrix}a& b\end{bmatrix}^T \) is the vector of weighting coefficients, and \( \mathrm{S} = \operatorname{cov}(x,y) = \begin{bmatrix}\sigma_x{}^2 & \rho\sigma_x\sigma_y \cr \rho\sigma_x\sigma_y & \sigma_y{}^2\end{bmatrix} \). Yep, there’s the covariance matrix again.)
def calc_dprime(distA,distB,projection): """ calculates dprime for two distributions, given a projection P = [cx,cy] that defines u = cx*x + cy*y """ distAp = distA.project(projection) distBp = distB.project(projection) return (distAp.mu - distBp.mu)/np.sqrt( (distAp.sigma**2 + distBp.sigma**2)/2.0 ) def show_dprime(distA, distB, a,b): print "u=%.6fx%+.6fy" % (a,b) x = np.arange(0,100,0.1) fig = plt.figure() ax = fig.add_subplot(1,1,1) for projname, projection, linestyle in [ ('x','x',':'), ('y','y','--'), ('u',[a,b],'-')]: distAp = distA.project(projection) distBp = distB.project(projection) dprime = calc_dprime(distA, distB, projection) print "dprime(%s)=%.4f" % (projname,dprime) for dist in [distAp,distBp]: ax.plot(x,dist.pdf(x), color=dist.color, linestyle=linestyle, label='$%s$: %s, $\\mu=$%.1f, $\\sigma=$%.2f' % (projname, dist.id, dist.mu, dist.sigma)) ax.set_ylabel('probability density') ax.set_xlabel('measurement $(x,y,u)$') ax.set_ylim(0,0.15) ax.legend(labelspacing=0, fontsize=10,loc='upper left'); show_dprime(distA, distB, -0.88,1.88)
u=-0.880000x+1.880000y dprime(x)=2.6747 dprime(y)=4.4849 dprime(u)=5.1055
We can get a better separation between alternatives, as measured by \( d’ \), through this linear combination of \( x \) and \( y \) than by either one alone. What’s going on, and where did the equation \( u=-0.88x + 1.88y \) come from?
Can we do better than that? How about \( u=-0.98x + 1.98y \)? or \( u=-0.78x + 1.78y \)?
show_dprime(distA, distB, -0.98,1.98)
u=-0.980000x+1.980000y dprime(x)=2.6747 dprime(y)=4.4849 dprime(u)=5.0997
show_dprime(distA, distB, -0.78,1.78)
u=-0.780000x+1.780000y dprime(x)=2.6747 dprime(y)=4.4849 dprime(u)=5.0988
Hmm. These aren’t quite as good; the value for \( d’ \) is lower. How do we know how to maximize \( d’ \)?
Begin grungy algebra
There doesn’t look like a simple intuitive way to find the best projection. At first I thought of modeling this as \( v = x \cos\theta + y \sin\theta \) for some angle \( \theta \). But this didn’t produce any easy answer. I muddled my way to an answer by looking for patterns that helped to cancel out some of the grunginess.
One way to maximize \( d’ \) is to write it as a function of \( \theta \) with \( v=ax+by, a = a_1\cos \theta+a_2\sin\theta, b = b_1\cos\theta+b_2\sin\theta \) for some convenient \( a_1, a_2, b_1, b_2 \) to make the math nice. We’re going to figure out \( d’ \) as a function of \( a,b \) in general first:
$$\begin{aligned} d’ &= \frac{\mu_{vA} - \mu_{vB}}{\sqrt{\frac{1}{2}(\sigma_{vA}{}^2 + \sigma_{vB}{}^2)}} \cr &= \frac{a(\mu_{xA}-\mu_{xB})+b(\mu_{yA} - \mu_{yB})}{\sqrt{\frac{1}{2}(a^2(\sigma_{xA}^2 + \sigma_{xB}^2) + 2ab(\rho_A\sigma_{xA}\sigma_{yA} + \rho_B\sigma_{xB}\sigma_{yB}) + b^2(\sigma_{yA}^2+\sigma_{yB}^2))}} \cr &= \frac{a(\mu_{xA}-\mu_{xB})+b(\mu_{yA} - \mu_{yB})}{\sqrt{\frac{1}{2}f(a,b)}} \cr \end{aligned}$$
with \( f(a,b) = a^2(\sigma_{xA}^2 + \sigma_{xB}^2) + 2ab(\rho_A\sigma_{xA}\sigma_{yA} + \rho_B\sigma_{xB}\sigma_{yB}) + b^2(\sigma_{yA}^2+\sigma_{yB}^2). \)
Yuck.
Anyway, if we can make the denominator constant as a function of \( \theta \), then the numerator is easy to maximize.
If we define
$$\begin{aligned} K_x &= \sqrt{\sigma_{xA}^2 + \sigma_{xB}^2} \cr K_y &= \sqrt{\sigma_{yA}^2 + \sigma_{yB}^2} \cr R &= \frac{\rho_A\sigma_{xA}\sigma_{yA} + \rho_B\sigma_{xB}\sigma_{yB}}{K_xK_y} \end{aligned}$$
then \( f(a,b) = a^2K_x{}^2 + 2abRK_xK_y + b^2K_y{}^2 \) which is easier to write than having to carry around all those \( \mu \) and \( \sigma \) terms.
If we let \( a = \frac{1}{\sqrt{2}K_x}(c \cos \theta + s \sin\theta) \) and \( b = \frac{1}{\sqrt{2}K_y}(c \cos \theta - s\sin\theta) \) then
$$\begin{aligned} f(a,b) &= \frac{1}{2}(c^2 \cos^2\theta + s^2\sin^2\theta + 2cs\cos\theta\sin\theta) \cr &+ \frac{1}{2}(c^2 \cos^2\theta + s^2\sin^2\theta - 2cs\cos\theta\sin\theta) \cr &+R(c^2 \cos^2\theta - s^2\sin^2\theta) \cr &= (1+R)c^2 \cos^2\theta + (1-R)s^2\sin^2\theta \end{aligned}$$
which is independent of \( \theta \) if \( (1+R)c^2 = (1-R)s^2 \). If we let \( c = \cos \phi \) and \( s=\sin \phi \) then some nice things all fall out:
- \( f(a,b) \) is constant if \( \tan^2\phi = \frac{1+R}{1-R} \), in other words \( \phi = \tan^{-1} \sqrt{\frac{1+R}{1-R}} \)
- \( c = \cos\phi = \sqrt{\frac{1-R}{2}} \) (hint: use the identities \( \sec^2 \theta = \tan^2 \theta + 1 \) and \( \cos \theta = 1/\sec \theta \))
- \( s = \sin\phi = \sqrt{\frac{1+R}{2}} \)
- \( f(a,b) = (1-R^2)/2 \)
- \( a = \frac{1}{\sqrt{2}K_x}\cos (\theta - \phi) = \frac{1}{\sqrt{2}K_x}(\cos \phi \cos \theta + \sin\phi \sin\theta)= \frac{1}{2K_x}(\sqrt{1-R} \cos \theta + \sqrt{1+R} \sin\theta) \)
- \( b = \frac{1}{\sqrt{2}K_y}\cos (\theta + \phi) = \frac{1}{\sqrt{2}K_y}(\cos \phi \cos \theta - \sin\phi \sin\theta)= \frac{1}{2K_y}(\sqrt{1-R} \cos \theta - \sqrt{1+R} \sin\theta) \)
and when all is said and done we get
$$\begin{aligned} d’ &= \frac{a(\mu_{xA}-\mu_{xB})+b(\mu_{yA} - \mu_{yB})}{\sqrt{\frac{1}{2}f(a,b)}} \cr &= \frac{a(\mu_{xA}-\mu_{xB})+b(\mu_{yA} - \mu_{yB})}{\frac{1}{2}\sqrt{1-R^2}} \cr &= K_c \cos\theta + K_s \sin\theta \end{aligned}$$
if
$$\begin{aligned} \delta_x &= \frac{\mu_{xA}-\mu_{xB}}{K_x} = \frac{\mu_{xA}-\mu_{xB}}{\sqrt{\sigma_{xA}^2 + \sigma_{xB}^2}} \cr \delta_y &= \frac{\mu_{yA} - \mu_{yB}}{K_y} = \frac{\mu_{yA} - \mu_{yB}}{\sqrt{\sigma_{yA}^2 + \sigma_{yB}^2}} \cr K_c &= \sqrt{\frac{1-R}{1-R^2}} \left(\delta_x + \delta_y \right) \cr &= \frac{1}{\sqrt{1+R}} \left(\delta_x + \delta_y \right) \cr K_s &= \sqrt{\frac{1+R}{1-R^2}} \left(\delta_x - \delta_y \right) \cr &= \frac{1}{\sqrt{1-R}} \left(\delta_x - \delta_y \right) \cr \end{aligned}$$
Then \( d’ \) has a maximum value of \( D = \sqrt{K_c{}^2 + K_s{}^2} \) at \( \theta = \tan^{-1}\dfrac{K_s}{K_c} \), where \( \cos \theta = \dfrac{K_c}{\sqrt{K_s^2 + K_c^2}} \) and \( \sin \theta = \dfrac{K_s}{\sqrt{K_s^2 + K_c^2}}. \)
Plugging into \( a \) and \( b \) we get
$$\begin{aligned} a &= \frac{1}{2K_x}(\sqrt{1-R} \cos \theta + \sqrt{1+R} \sin\theta)\cr &= \frac{1}{2K_x}\left(\frac{(1-R)(\delta_x+\delta_y)}{\sqrt{1-R^2}}+\frac{(1+R)(\delta_x-\delta_y)}{\sqrt{1-R^2}}\right)\cdot\frac{1}{\sqrt{K_s^2 + K_c^2}} \cr &= \frac{\delta_x - R\delta_y}{K_xD\sqrt{1-R^2}}\cr b &= \frac{1}{2K_y}(\sqrt{1-R} \cos \theta - \sqrt{1+R} \sin\theta)\cr &= \frac{1}{2K_y}\left(\frac{(1-R)(\delta_x+\delta_y)}{\sqrt{1-R^2}}-\frac{(1+R)(\delta_x-\delta_y)}{\sqrt{1-R^2}}\right)\cdot\frac{1}{\sqrt{K_s^2 + K_c^2}} \cr &= \frac{-R\delta_x + \delta_y}{K_yD\sqrt{1-R^2}} \end{aligned}$$
We can also solve \( D \) in terms of \( \delta_x, \delta_y, \) and \( R \) to get
$$\begin{aligned} D &= \frac{1}{\sqrt{1-R^2}}\sqrt{(1-R)(\delta_x+\delta_y)^2 + (1+R)(\delta_x-\delta_y)^2} \cr &= }} \end{aligned}$$
Let’s try it!
Kx = np.hypot(distA.sigma_x,distB.sigma_x) Ky = np.hypot(distA.sigma_y,distB.sigma_y) R = (distA.rho*distA.sigma_x*distA.sigma_y + distB.rho*distB.sigma_x*distB.sigma_y)/Kx/Ky Kx, Ky, R
(7.9309520235593407, 6.6219332524573211, 0.86723211589363869)
dmux = (distA.mu_x - distB.mu_x)/Kx dmuy = (distA.mu_y - distB.mu_y)/Ky Kc = (dmux + dmuy)/np.sqrt(1+R) Ks = (dmux - dmuy)/np.sqrt(1-R) Kc,Ks
(3.7048851247525367, -3.5127584699841927)
theta = np.arctan(Ks/Kc) a = 1.0/2/Kx*(np.sqrt(1-R)*np.cos(theta) + np.sqrt(1+R)*np.sin(theta) ) b = 1.0/2/Ky*(np.sqrt(1-R)*np.cos(theta) - np.sqrt(1+R)*np.sin(theta) ) dprime = np.hypot(Kc,Ks) dprime2 = Kc*np.cos(theta) + Ks*np.sin(theta) assert abs(dprime - dprime2) < 1e-7 delta_x = (distA.mu_x - distB.mu_x)/np.hypot(distA.sigma_x,distB.sigma_x) delta_y = (distA.mu_y - distB.mu_y)/np.hypot(distA.sigma_y,distB.sigma_y) dd = np.sqrt(2*delta_x**2 - 4*R*delta_x*delta_y + 2*delta_y**2) dprime3 = dd/np.sqrt(1-R*R) assert abs(dprime - dprime3) < 1e-7 a2 = (delta_x - R*delta_y)/Kx/dd b2 = (-R*delta_x + delta_y)/Ky/dd assert abs(a-a2) < 1e-7 assert abs(b-b2) < 1e-7 print "theta=%.6f a=%.6f b=%.6f d'=%.6f" % (theta, a, b, dprime) # scale a,b such that their sum is 1.0 print " also a=%.6f b=%.6f is a solution with a+b=1" % (a/(a+b), b/(a+b))
theta=-0.758785 a=-0.042603 b=0.090955 d'=5.105453 also a=-0.881106 b=1.881106 is a solution with a+b=1
And out pops \( u\approx -0.88x + 1.88y \).
End grungy algebra
What if we use \( u=-0.8811x + 1.8811y \) as a way to combine the results of tests \( T_1 \) and \( T_2 \)? Here is a superposition of lines with constant \( u \):
# Lines of constant u fig = plt.figure() ax = fig.add_subplot(1,1,1) separation_plot((xA,yA,distA),(xB,yB,distB), Q, L, ax=ax) xmax = ax.get_xlim()[1] ymax = ax.get_ylim()[1] ua = a/(a+b) ub = b/(a+b) for u in np.arange(ua*xmax,ub*ymax+0.01,10): x1 = min(xmax,(u-ub*ymax)/ua) x0 = max(0,u/ua) x = np.array([x0,x1]) ax.plot(x,(u-ua*x)/ub,color='orange')
To summarize:
$$\begin{aligned} R &= \frac{\rho_A\sigma_{xA}\sigma_{yA} + \rho_B\sigma_{xB}\sigma_{yB}}{\sqrt{(\sigma_{xA}^2 + \sigma_{xB}^2)(\sigma_{yA}^2 + \sigma_{yB}^2)}} \cr \delta_x &= \frac{\mu_{xA}-\mu_{xB}}{\sqrt{\sigma_{xA}^2 + \sigma_{xB}^2}} \cr \delta_y &= \frac{\mu_{yA} - \mu_{yB}}{\sqrt{\sigma_{yA}^2 + \sigma_{yB}^2}} \cr \max d’ = D &= }}\cr \end{aligned}$$
and we can calculate a new derived measurement \( u=ax+by \) which has separation coefficient \( d’ \) between its distributions under the conditions \( A \) and \( B \).
u = np.arange(0,100,0.1) projAB = [-0.8811, 1.8811] distA_T1T2lin = distA.project(projAB) distB_T1T2lin = distB.project(projAB) show_binary_pdf(distA_T1T2lin, distB_T1T2lin, y, xlabel = '$u = %.4fx + %.4fy$' % tuple(projAB)) for false_negative_cost in [10e6, 100e6]: value_matrix_T2 = np.array([[0,-5000],[-false_negative_cost, -1e5]]) - 100 threshold_info = find_threshold(distB_T1T2lin, distA_T1T2lin, Pa_total, value_matrix_T2) u0 = [uval for uval,_ in threshold_info if uval > 20 and uval < 80][0] C = analyze_binary(distB_T1T2lin, distA_T1T2lin, u0) print "False negative cost = $%.0fM" % (false_negative_cost/1e6) display(show_binary_matrix(C, 'u_0=ax+by=%.2f' % u0, [distB_T1T2lin, distA_T1T2lin], 'ba', Pa_total, value_matrix_T2, special_format={'v':'$%.2f'})) info = gather_info(C,value_matrix_T2,Pa_total,u0=u0) if false_negative_cost == 10e6: info57 = info else: info58 = info
False negative cost = $10M
Report for threshold \(u_0=ax+by=50.42 \rightarrow E[v]=\)$-119.26
False negative cost = $100M
Report for threshold \(u_0=ax+by=48.22 \rightarrow E[v]=\)$-144.54
One final subtlety
Before we wrap up the math, there’s one more thing that is worth a brief mention.
When we use both tests with the quadratic function \( \lambda(x,y) \), there’s a kind of funny region we haven’t talked about. Look on the graph below, at point \( P = (x=40, y=70) \):
fig = plt.figure() ax = fig.add_subplot(1,1,1) separation_plot((xA,yA,distA),(xB,yB,distB), Q, L, ax=ax) P=Coordinate2D(40,70) ax.plot(P.x,P.y,'.',color='orange') Ptext = Coordinate2D(P.x-10,P.y) ax.text(Ptext.x,Ptext.y,'$P$',fontsize=20, ha='right',va='center') ax.annotate('',xy=P,xytext=Ptext, arrowprops=dict(facecolor='black', width=1, headwidth=5, headlength=8, shrink=0.05));
This point is outside the contour \( \lambda_{10} > L_{10} \), so that tells us we should give a diagnosis of EP-negative. But this point is closer to the probability “cloud” of EP-positive. Why?
for dist in [distA, distB]: print("Probability density at P of %s = %.3g" % (dist.name, dist.pdf(P.x,P.y))) print(dist)
Probability density at P of A (EP-positive) = 6.28e-46 Gaussian(mu_x=55, mu_y=57, sigma_x=5.3, sigma_y=4.1, rho=0.91, name='A (EP-positive)', id='A', color='red') Probability density at P of B (EP-negative) = 2.8e-34 Gaussian(mu_x=40, mu_y=36, sigma_x=5.9, sigma_y=5.2, rho=0.84, name='B (EP-negative)', id='B', color='#8888ff')
The probability density is smaller at P for the EP-positive case, even though this point is closer to the corresponding probability distribution. This is because the distribution is narrower; \( \sigma_x \) and \( \sigma_y \) are both smaller for the EP-positive case.
As a thought experiment, imagine the following distributions A and B, where B is very wide (\( \sigma=5 \)) compared to A (\( \sigma = 0.5 \)):
dist_wide = Gaussian1D(20,5,'B (wide)',id='B',color='green') dist_narrow = Gaussian1D(25,0.5,'A (narrow)',id='A',color='red') x = np.arange(0,40,0.1) show_binary_pdf(dist_wide, dist_narrow, x) plt.xlabel('x');
In this case, if we take some sample measurement \( x \), a classification of \( A \) makes sense only if the measured value \( x \) is near \( A \)’s mean value \( \mu=25 \), say from 24 to 26. Outside that range, a classification of \( B \) makes sense, not because the measurement is closer to the mean of \( B \), but because the expected probability of \( B \) given \( x \) is greater. This holds true even for values within a few standard deviations from the mean, like \( x=28 = \mu_B + 1.6\sigma_B \), because the distribution of \( A \) is so narrow.
We’ve been proposing tests where there is a single threshold — for example diagnose as \( a \) if \( x > x_0 \), otherwise diagnose as \( b \) — but there are fairly simple cases where two thresholds are required. In fact, this is true in general when the standard deviations are unequal; if you get far enough away from the means, the probability of the wider distribution is greater.
You might think, well, that’s kind of strange, if I’m using the same piece of equipment to measure all the sample data, why would the standard deviations be different? A digital multimeter measuring voltage, for example, has some inherent uncertainty. But sometimes the measurement variation is due to differences in the populations themselves. For example, consider the wingspans of two populations of birds, where \( A \) consists of birds that are pigeons and \( B \) consists of birds that are not pigeons. The \( B \) population will have a wider range of measurements simply because this population is more heterogeneous.
Please note, by the way, that the Python functions I wrote to analyze the bivariate Gaussian situation make the assumption that the standard deviations are unequal and the log-likelihood ratio \( \lambda(x,y) \) is either concave upwards or concave downwards — in other words, the \( A \) distribution has lower values of both \( \sigma_x \) and \( \sigma_y \) than the \( B \) distribution, or it has higher values of both \( \sigma_x \) and \( \sigma_y \). In these cases, the contours of constant \( \lambda \) are ellipses. In general, they may be some other conic section (lines, parabolas, hyperbolas) but I didn’t feel like trying to achieve correctness in all cases, for the purposes of this article.
So which test is best?
Let’s summarize the tests we came up with. We have 10 different tests, namely each of the following with false-negative costs of \$10 million and \$100 million:
- test \( T_1 \) only
- tests \( T_1 \) and \( T_2 \) – quadratic function of \( x,y \)
- test \( T_1 \) first, then \( T_2 \) if needed
- test \( T_2 \) only
- tests \( T_1 \) and \( T_2 \) – linear function of \( x,y \)
import pandas as pd def present_info(info): C = info['C'] J = info['J'] V = info['V'] if 'x0' in info: threshold = '\\( x_0 = %.2f \\)' % info['x0'] t = 1 Bb1 = J[0,0] Bb2 = 0 elif 'xL' in info: threshold = ('\\( x_L = %.2f, x_H=%.2f, L_{10}=%.4f \\)' % (info['xL'],info['xH'],info['L']/np.log(10))) t = 3 Bb1 = J[0,0] Bb2 = J[0,1] elif 'L' in info: threshold = '\\( L_{10}=%.4f \\)' % (info['L']/np.log(10)) t = 2 Bb1 = 0 Bb2 = J[0,0] elif 'y0' in info: threshold = '\\( y_0 = %.2f \\)' % info['y0'] t = 4 Bb1 = 0 Bb2 = J[0,0] elif 'u0' in info: threshold = '\\( u_0 = ax+by = %.2f \\)' % info['u0'] t = 4 Bb1 = 0 Bb2 = J[0,0] nc = J.shape[1] return {'Exp. cost':'$%.2f' % (-J*V).sum(), 'Threshold': threshold, 'N(Ab)': int(np.round(10e6*J[1,:nc//2].sum())), 'N(Ba)': int(np.round(10e6*J[0,nc//2:].sum())), 'N(Aa)': int(np.round(10e6*J[1,nc//2:].sum())), 'P(b|A)': '%.2f%%' % (C[1,:nc//2].sum() * 100), 'P(Bb,$0)': '%.2f%%' % (Bb1*100), 'P(Bb,$100)': '%.2f%%' % (Bb2*100), } tests = ['\\(T_1\\)', '\\(T_1 + T_2\\)', '\\(T_1 \\rightarrow T_2 \\)', '\\(T_2\\)', '\\(T_1 + T_2\\) (linear)'] print "Exp. cost = expected cost above test T1 ($1)" print "N(Aa) = expected number of correctly-diagnosed EP-positives per 10M patients" print "N(Ab) = expected number of false negatives per 10M patients" print "N(Ba) = expected number of false positives per 10M patients" print("P(Bb,$0) = percentage of patients correctly diagnosed EP-negative,\n"+ " no additional cost after test T1") print("P(Bb,$100) = percentage of patients correctly diagnosed EP-negative,\n"+ " test T2 required") print "P(b|A) = conditional probability of a false negative for EP-positive patients" print "T1 -> T2: test T1 followed by test T2 if needed" df = pd.DataFrame([present_info(info) for info in [info17,info27,info37,info47,info57, info18,info28,info38,info48,info58]], index=['\\$%dM, %s' % (cost,test) for cost in [10,100] for test in tests]) colwidths = [12,10,7,7,10,10,10,10,24] colwidthstyles = [{'selector':'thead th.blank' if i==0 else 'th.col_heading.col%d' % (i-1), 'props':[('width','%d%%'%w)]} for i,w in enumerate(colwidths)] df.style.set_table_styles([{'selector':' ','props': {'width':'100%', 'table-layout':'fixed', }.items()}, {'selector':'thead th', 'props':[('font-size','90%')]}, {'selector': 'td span.MathJax_CHTML,td span.MathJax,th span.MathJax_CHTML,th span.MathJax', 'props':[('white-space','normal')]}, {'selector':'td.data.col7', 'props':[('font-size','90%')]}] + colwidthstyles)
Exp. cost = expected cost above test T1 ($1) N(Aa) = expected number of correctly-diagnosed EP-positives per 10M patients N(Ab) = expected number of false negatives per 10M patients N(Ba) = expected number of false positives per 10M patients P(Bb,$0) = percentage of patients correctly diagnosed EP-negative, no additional cost after test T1 P(Bb,$100) = percentage of patients correctly diagnosed EP-negative, test T2 required P(b|A) = conditional probability of a false negative for EP-positive patients T1 -> T2: test T1 followed by test T2 if needed
There! We can keep expected cost down by taking the \( T_1 \rightarrow T_2 \) approach (test 2 only if \( x_L \le x \le x_H \)).
With \$10M cost of a false negative, we can expect over 81% of patients will be diagnosed correctly as EP-negative with just the \$1 cost of the eyeball photo test, and only 18 patients out of ten million (4.5% of EP-positive patients) will experience a false negative.
With \$100M cost of a false negative, we can expect over 55% of patients will be diagnosed correctly as EP-negative with just the \$1 cost of the eyeball photo test, and only 3 patients out of ten million (0.7% of EP-positive patients) will experience a false negative.
And although test \( T_2 \) alone is better than test \( T_1 \) alone, both in keeping expected costs down, and in reducing the incidence of both false positives and false negatives, it’s pretty clear that relying on both tests is the most attractive option.
There is not too much difference between the combination of tests \( T_1+T_2 \) using \( \lambda_{10}(x,y) > L_{10} \) as a quadratic function of \( x \) and \( y \) based on the logarithm of the probability density functions, and a linear function \( u = ax+by > u_0 \) for optimal choices of \( a,b \). The quadratic function has a slightly lower expected cost.
What the @%&^ does this have to do with embedded systems?
We’ve been talking a lot about the mathematics of binary classification based on a two-test set of measurements with measurement \( x \) from test \( T_1 \) and measurement \( y \) from test \( T_2 \), where the probability distributions over \( (x,y) \) are a bivariate normal (Gaussian) distribution with slightly different values of mean \( (\mu_x, \mu_y) \) and covariance matrix \( \begin{bmatrix}\sigma_x{}^2 & \rho\sigma_x\sigma_y \cr \rho\sigma_x\sigma_y & \sigma_y{}^2\end{bmatrix} \) for two cases \( A \) and \( B \).
As an embedded system designer, why do you need to worry about this?
Well, you probably don’t need the math directly. It is worth knowing about different ways to use the results of the tests.
The more important aspect is knowing that a binary outcome based on continuous measurements throws away information. If you measure a sensor voltage and sound an alarm if the sensor voltage \( V > V_0 \) but don’t sound the alarm if \( V \le V_0 \) then this doesn’t distinguish the case of \( V \) being close to the threshold \( V_0 \) from the case where \( V \) is far away from the threshold. We saw this with idiot lights. Consider letting users see the original value \( V \) as well, not just the result of comparing it with the threshold. Or have two thresholds, one indicating a warning and the second indicating an alarm. This gives the user more information.
Be aware of the tradeoffs in choosing a threshold — and that someone needs to choose a threshold. If you lower the false positive rate, the false negative rate will increase, and vice versa.
Finally, although we’ve emphasized the importance of minimizing the chance of a false negative (in our fictional embolary pulmonism example, missing an EP-positive diagnosis may cause the patient to die), there are other costs to false positives besides inflicting unnecessary costs on users/patients. One that occurs in the medical industry is “alarm fatigue”, which is basically a loss of confidence in equipment/tests that cause frequent false positives. It is the medical device equivalent to the Aesop’s fable about the boy who cried wolf. One 2011 article stated it this.
One solution may be to abandon the ever-present beep and use sounds that have been designed to reduce alarm fatigue.
The real takeaway here is that the human-factors aspect of a design (how an alarm is presented) is often as important or even more important than the math and engineering behind the design (how an alarm is detected). This is especially important in safety-critical situations such as medicine, aviation, nuclear engineering, or industrial machinery.
References
- The accuracy of yes/no classification, University of Pennsylvania
- Sensitivity and Bias - an introduction to Signal Detection Theory, University of Birmingham
- Signal Detection Theory, New York University
- D-prime (signal detection) analysis, University of California at Los Angeles
- Calculation of signal detection theory measures, Stanislaw and Todorov, Behavior Research Methods, Instruments, & Computers, March 1999
Wrapup
We’ve talked in great detail today about binary outcome tests, where one or more continuous measurements are used to detect the presence of some condition \( A \), whether it’s a disease, or an equipment failure, or the presence of an intruder.
- False positives are when the detector erroneously signals that the condition is present. (consequences: annoyance, lost time, unnecessary costs and use of resources)
- False negatives are when the detector erroneously does not signal that the condition is present. (consequences: undetected serious conditions that may get worse)
- Choice of a threshold can trade off false positive and false negative rates
- Understanding the base rate (probability that the condition occurs) is important to avoid the base rate fallacy
- If the probability distribution of the measurement is a normal (Gaussian) distribution, then an optimal threshold can be chosen to maximize expected value, by using the logarithm of the probability density function (PDF), given:
- the first- and second-order statistics (mean and standard deviation for single-variable distributions) of both populations with and without condition \( A \)
- knowledge of the base rate
- estimated costs of all four outcomes (true positive detection, false positive, false negative, true negative)
- A binary outcome test can be examined in terms of a confusion matrix that shows probabilities of all four outcomes
- We can find the optimal threshold by knowing that if a measurement occurs at the optimal threshold, both positive and negative diagnoses have the same expected value, based the conditional probability of occurrence given the measured value
- Bayes’ Rule can be used to compute the conditional probability of \( A \) given the measured value, from its “converse”, the conditional probability of the measured value with and without condition \( A \)
- Idiot lights, where the detected binary outcome is presented instead of the original measurement, hide information from the user, and should be used with caution
- The distinguishability or separation coefficient \( d’ \) can be used to characterize how far apart two probability distributions are, essentially measuring the difference of the means, divided by an effective standard deviation
- If two tests are possible, with an inexpensive test \( T_1 \) offering a mediocre value of \( d’ \), and a more expensive test \( T_2 \) offering a higher value of \( d’ \), then the two tests can be combined to help reduce overall expected costs. We explored one situation (the fictional “embolary pulmonism” or EP) where the probability distribution was a known bivariate normal distribution. Five methods were used, in order of increasing effectiveness:
- Test \( T_1 \) only, producing a measurement \( x \), detecting condition \( A \) if \( x>x_0 \) (highest expected cost)
- Test \( T_2 \) only, producing a measurement \( y \), detecting condition \( A \) if \( y>y_0 \)
- Test \( T_1 \) and \( T_2 \), combined by a linear combination \( u = ax+by \), detecting condition \( A \) if \( u>u_0 \), with \( a \) and \( b \) chosen to maximize \( d’ \)
- Test \( T_1 \) and \( T_2 \), combined by a quadratic function \( \lambda(x,y) = a(x-\mu_x)^2 + b(x-\mu_x)(y-\mu_y) + c(y-\mu_y)^2 \) based on the log of the ratio of PDFs, detecting condition \( A \) if \( \lambda(x,y) > L \) (in our example, this has a slightly lower cost than the linear combination)
- Test \( T_1 \) used to detect three cases based on thresholds \( x_L \) and \( x_H \) (lowest expected cost):
- Diagnose absense of condition \( A \) if \( x < x_L \), no further test necessary
- Diagnose presence of condition \( A \) if \( x > x_H \), no further test necessary
- If \( x_L \le x \le x_H \), perform test \( T_2 \) and diagnose based on the measurements from both tests (we explored using the quadratic function in this article)
- An excessive false positive rate can cause “alarm fatigue” in which true positives may be missed because of a tendency to ignore detected conditions
Whew! OK, that’s all for now.
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Wye Delta Tee Pi: Observations on Three-Terminal Networks
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Jaywalking Around the Compiler
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C++ Method Overloading Program
Hello Everyone!
In this tutorial, we will learn how to demonstrate the concept of Method Overloading, in the C++ programming language.
To understand the concept of Method or Function Overloading in CPP, we will recommend you to visit here: Function Overriding, where we have explained it from scratch.
Code:
#include <iostream> #include <vector> using namespace std; //defining the class shape to overload the method area() on the basis of number of parameters. class shape { //declaring member variables public: int l, b, s; //defining member function or methods public: void input() { cout << "Enter the length of each side of the Square: \n"; cin >> s; cout << "\n"; cout << "Enter the length and breadth of the Rectangle: \n"; cin >> l >> b; cout << "\n"; } //Demonstrating Method Overloading public: void area(int side) { cout << "Area of Square = " << side * side; cout << "\n"; } void area(int length, int breadth) { cout << "Area of Rectangle = " << length * breadth; cout << "\n"; } }; //Defining the main method to access the members of the class int main() { cout << "\n\nWelcome to Studytonight :-)\n\n\n"; cout << " ===== Program to demonstrate Method Overloading in a Class, in CPP ===== \n\n"; //Declaring class object to access class members from outside the class shape sh; cout << "\nCalling the input() function to take the values from the user\n"; sh.input(); cout << "\nCalling the area(int) function to calculate the area of the Square\n"; sh.area(sh.s); cout << "\nCalling the area(int,int) function to calculate the area of the Rectangle\n"; sh.area(sh.l, sh.b); cout << "\nExiting the main() method\n\n\n"; return 0; }
Output:
We hope that this post helped you develop a better understanding of the concept of Method Overloading in C++. For any query, feel free to reach out to us via the comments section down below.
Keep Learning : ) | https://studytonight.com/cpp-programs/cpp-method-overloading-program | CC-MAIN-2021-04 | refinedweb | 303 | 56.83 |
Perils of DNS at RIPE-52 71
An anonymous reader wrote in to say that " The RIPE meeting got off to a good start yesterday (for those of you outside Europe, RIPE is the European counterpart to ARIN). Emin Sirer from Cornell presented his study of DNS vulnerabilities. The results are staggering: the average name depends on four dozen nameservers, 30% of domains are vulnerable to domain hijacks by simple script kiddies, 85% of domains are vulnerable to hijacks by attackers that can DoS two hosts. The lesson: DNS must be managed by professionals, and the pros have to pay attention to the DNS delegation graph when they set up name servers."
Associated paper with more details. (Score:4, Informative)
Re:Associated paper with more details. (Score:4, Interesting)
1. Nameservers give correct version information. This is not correct, some intentionally mislead.
2. Nameservers of a certain version string all have certain vulnerabilities. This is not correct, there are dependencies on platform/OS. Also see 1.
3. DNS Clients are dumb. What I mean here is that no credit is given to the DNS client for discarding incorrect information. Some clients will bypass certain cache poisoning.
I appreciate what the paper is trying to say. Security vs usability is always a direct tradeoff. In the case of DNS, its biggest strength (massively distributed) is also its biggest security weakness.
Re:Associated paper with more details. (Score:4, Insightful)
Re:Associated paper with more details. (Score:3)
Meaning, if I as an attacker need to choose between two domains to attack, I would prefer the one that would give the biggest payoff for the least work. More namerservers means the attacker has to do more work for the same number of victims (redirected queries).
Re:Associated paper with more details. (Score:1)
Re:Associated paper with more details. (Score:3)
- Little analysis is given to the effect (in practice) of glue records. A footnote mentions that glue is not authoritative, but does not elaborate on how glue is actually used in the chain.
- TCB is a poor metric for assessing the attack profile with respect to a name. You talk in your comment about the vulnerabilities depending on the shape of the graph, and assert "In practice, DNS dependence graphs tend to be long and narrow." (not supported by
Re:Associated paper with more details. (Score:3)
From the talk: "It is a well-accepted axiom of computer security that a small trusted computing base is highly desirable: it is easier to secure, audit and manage."
The followup would be that a small TCB is also at more risk for failure.
Security, resilience or usability, pick two.
Re:Associated paper with more details. (Score:3)
Having more nameservers in the DNS chain means more of those servers need to be compromised to redirect the same number of requesters. Even better if those nameservers are diverse, so that one exploit wouldn't work on all of them.
Note from the author. (Score:5, Informative)
This survey was a lot of fun. It's sort of like a "how to 0wn the Internet via DNS" survey. In fact, that was the subtitle of my talk and was the most fun academic paper I ever wrote. It's all based on public information, by the way. The findings were quite surprising, at least to us.
First, the average DNS name depends on a large number of nameservers. Not just the two or three nameservers that you designate when you register the name, but also the nameservers those servers are served by, and so on. This set includes a few dozen hosts for the average
.COM domain. If you are in the Ukraine, Malaysia, Poland, or Italy, this set includes more than 400 hosts! In contrast, Japan (.jp) is run very well, and names in .jp depend on very few hosts.
Second, some names are incredibly vulnerable. The most vulnerable name in our survey, the Roman Catholic Church web site in the Ukraine, depends on servers in Berkeley, NYU, UCLA, Russia, Poland, Sweden, Norway, Germany, Austria, France , England, Canada, Israel, and Australia. It's possible to take over that Ukrainian website (and announce a new pope, perhaps?) by compromising a host in Monash, Australia. DNS makes a small world after all.
Typically, you can find some compromised hosts in the dependence graph, DoS the non-vulnerable hosts for a very short time when DNS glue is about to expire, and poison caches. Repeat and rinse until you have hijacked the name of your choice.
Finally, some nameservers are very valuable, they control a large percentage of names. Some of these valuable nameservers are in educational institutions, which have no fiduciary responsibility to the names they serve. In fact, folks at NYU may not be aware that they can control the entire namespace for Baltic countries under the right circumstances.
Interestingly, the FBI.GOV site was vulnerable. We reported this to the DHS and someone upgraded the nameserver involved. We suspect the vulnerability we found was a real one, though we did not attempt to take advantage of it so we can't tell for sure.
Our website has an active webserver [cornell.edu] where you can type in your favorite sitename, see its dependencies and vulnerabilities. The data is a snapshot we took when we performed this study; do not be surprised if it does not reflect changes you made in the last few months.
The takeaway from this study is that the conventional wisdom about DNS servers, which says "the more DNS servers you have, the merrier as you increase fault tolerance" is wrong. You increase fault tolerance at the cost of increasing your trusted computing base. If you don't pay attention, someone from Monash Australia can hijack your site, and you might not even notice.
My research group generally looks at how to build more resilient infrastructure services. We built a safety net for DNS [cornell.edu], a system for monitoring updates on the web [cornell.edu], and a system for avoiding SPAM on P2P filesharing networks [cornell.edu]. Check them out if you are interested in new distributed services for the Internet.
Re:Note from the author. (Score:1)
Re:Associated paper with more details. (Score:1)
* inability to notice that dns server is visible under many different ips (thats very often the case in Europe, and that leaded to false assumption about average of 100 hosts used blah blah blah)
* glue records attached to dns reply doesnot increase average of 100 hosts used blah blah
It's important, but far lesser than stated in paper.
Re:This also just in (Score:4, Informative)
Re:This also just in (Score:1)
You are, of course, correct, but it has always been like this. Emin Sirer's report strikes me as either:
1) Chicken Little - "The sky is falling! The sky is falling!"
or
2) A graduate student who needed something to write a paper about.
What's next? A hysterical report about how (gasp!) a root server could be compromised and we'd all be hosed? Duh! Talk about stating the obvious.
Re:This also just in (Score:3, Interesting)
It really isn't the same at all. You sort of hope/expect a root server to be very closely monitoring and controlled by a professional team, but once you start adding multiple links in the chain of varying security and on top of that throw in broken DNS resolvers (like the ones SBC/AT&T use that only cache one nameserver for a given domain... even if the name
More information -- paper (Score:3, Informative)
Re:More information -- paper (Score:2)
Unfortunately, transitive trust is dangerous anywhere. The first example that comes to mind is handing your card over to a retailer to swipe; while it's something that's attempting to be addressed, with chip and pin readers, people equipped in the right way (whether script kiddies in the original example or someone in store with a second or tapped cardswiper (or, presumably next wave, same for chip and pin readers) in mine) have the ability to abuse that trust an
BIND false versions (Score:4, Interesting)
Re:BIND false versions (Score:1)
Re:BIND false versions (Score:1)
1. I would expect the FBI to have a completely seperate infrastructure for their computing needs that have nothing to do with fbi.gov.
2. You really think the FBI is going to depend on Sprint for anything?
Re:BIND false versions (Score:1)
Re:BIND false versions (Score:2, Funny)
Re:BIND false versions (Score:1)
dig is your friend. (Score:4, Interesting)
Re:dig is your friend. (Score:4, Informative)
Re:dig is your friend. (Score:2)
Whois shows it's Pegasus Web Technologies, in Parsippany, NJ.
Re:dig is your friend. (Score:1)
Also , for those outside (and inside) of Europe (Score:4, Informative), the United States, and several islands in the Caribbean Sea and North Atlantic Ocean;
* Facilitates the development of policy decisions made by its members and the stakeholders in its region;
* Is a nonprofit, membership organization;
* Is governed by an executive board elected by its membership.
Ripe and ARIN (Score:1, Offtopic)
Re:Ripe and ARIN (Score:1, Informative)
American Registry for Internet Numbers (ARIN) - Home Page [arin.net]
Re:Ripe and ARIN (Score:3, Funny)
A small sample (Score:2)
How many lookups to get to the center? (Score:4, Insightful)
Ask one of the 13 root servers who is nameserver for
Get back (A-M).GTLD-SERVERS.NET, they thoughtfully include IPs
Now ask a GTLD who has futurequest.net
Get back (ns1-ns3).futurequest.net, includes IPs
Now ask ns1 who www is
It provides IP for www is 69.5.6.116
So I guess there were 30 IP addresses involved, but I don't see the arcane resolution problems that this paper talked about. Maybe
Is it a problem or just redundant systems (good)? (Score:4, Insightful)
If you (correctly) configure your systems, you'll have 3 different DNS boxes on 3 different networks so any single problem won't take all of them out.
Okay, that does mean that you've just increased your attack visibility by 3x, but
And yes, if an attacker can get control of 1 of those boxes and DDoS the other 2 then he can redirect those queries to whatever box he wants to.
Re:Is it a problem or just redundant systems (good (Score:2)
While more servers may increase the number of exploits (I question this), that does not mean suddenly the attacker can get more overall exploit value out of those servers.
I suppose you would argue all the DNS eggs should be in one basket?
Re:Is it a problem or just redundant systems (good (Score:2)
You disregard that as the number of servers increases, the exploit value of each server is less. Meaning, with more servers it is more work to get the same exploit value.
Not really. The unhacked DNS servers can be DOSed. The attacker probably can't force all lookups to the hacked box, but if he can shut down the other DNS servers enough to get most of the lookups, that's almost as good.
Re:Is it a problem or just redundant systems (good (Score:1)
I consider a DOS'ed DNS server the same as exploited.
Further, DOSing sends up a red flag, the last thing an attacker wants is more attention.
Re:Is it a problem or just redundant systems (good (Score:2)
I consider a DOS'ed DNS server the same as exploited.
It is a form of exploit, but a simple DOS attack just makes the service unavailable. Coupling the hacking of a vulnerable server with a DOS on the other servers allows the attacker to redirect users and do some real damage.
Further, DOSing sends up a red flag, the last thing an attacker wants is more attention.
But the red flag is visible to the sysadmins managing the DNS servers, not to the poor schmuck who's getting sent to the attacker's copy of
Re:How many lookups to get to the center? (Score:1)
Not news, RIPE itself also to blame (Score:1)
And (not RIPE related) why the hell is
.pl - one of most vulnerable? (Score:3, Informative)
The part which I have emphasized gives us a hint: in Poland there is a tradition of unreliable telecommunications network. The biggest operator is a post-communistic ineffective giant delivering low quality of service. Therefore most businesses have developed a workaround - redundancy. Many registrars (DNS operators) are also Tier-2 ISPs and have links to most polish Tier-1 ISPs. When in reality they have 1 DNS server it can show up as many IP addresses, one for every Tier-1 ISP. And this is not taken into account by this survey, as far as I have gathered from a quick glance.
slashdot.org is vulnerable? (Score:2)
Re:slashdot.org is vulnerable? (Score:1)
Don't worry! Anyone stealing the slashdot.org name to redirect users to his own server will surely be slashdotted at once.
Someone just needs to want change bad enough. (Score:3, Interesting)
The bigger problem is clearly TRUST and can be alleviated if the DNS system was simply reimplemented. Easier said that done, yes, but a p2p with a trust metric system applied isn't overtly complicated and would scale. For instance, lets say you want example.com. It would be delegated when you register, propogated by it's trust amongst the root servers and the two or more namservers you've added when you've signed up. You then setup the trust system algo to prevent large attacks or changes.
The benefits are numerous, the roots are still the roots but are less taxed; their main purpose? The ultimate in trust so that subsequent nameservers always follow the trust metric and should a rogue amount decide to disobey trust metric they are flagged and dropped.
The only problem is actually doing it and setting up some sort of migration path.
Re:Someone just needs to want change bad enough. (Score:2, Informative)
Interestingly, the same research group cited in the story has built precisely such a system, a P2P replacement for DNS [cornell.edu]. It even has a migration path from the current DNS, supports the legacy namespace, and wo
Re:Someone just needs to want change bad enough. (Score:2)
real threats (Score:2)
Attacker could use DNS to relay virus payload to host, thus entirely bypassing NIDS systems.
Any command that resolves hostname could be used to exploit this concept.
It's not commonly used because the limited length of hostnames would require several
queries to transfer larger payloads.
But with some time and effort, attacker could hide the transfer almost completely.
There was an article about this on phrack? around 199x so
Counting ALL root servers? (Score:2)
It seems to me that it would be more accurate to only count 1 server at each level of the hierarchy as Dependent, and all the peers at that level as Redundant (co-dependent?).
The lesson (Score:3, Funny)
That's why I go with Network Solutions!
Well then... (Score:2)
That's nice to know. Then what is ARIN?
Re:Well then... (Score:1)
People who hand out blocks of IP addresses and keep track who has what.
Known to most of people through situations like whois -h whois.arin.net 11.22.33.44
RIPE != RIPE-NCC (Score:3, Informative)
Re:RIPE != RIPE-NCC (Score:2)
DNSSEC, anyone? (Score:1, Interesting) | https://it.slashdot.org/story/06/04/26/1247240/perils-of-dns-at-ripe-52 | CC-MAIN-2017-39 | refinedweb | 2,616 | 64.1 |
#include <envelopes.h>
Peak-hold filter.
The size is variable, and can be changed instantly with
.set(), or by using
.push()/
.pop() in an unbalanced way.
This has complexity O(1) every sample when the length remains constant (balanced
.push()/
.pop(), or using
filter(v)), and amortised O(1) complexity otherwise. To avoid allocations while running, it pre-allocates a vector (not a
std::deque) which determines the maximum length.
Sets the size immediately.
Must be
0 <= newSize <= maxLength (see constructor and
.resize()).
Shrinking doesn't destroy information, and if you expand again (with
preserveCurrentPeak=false), you will get the same output as before shrinking. Expanding when
preserveCurrentPeak is enabled is destructive, re-writing its history such that the current output value is unchanged. | https://signalsmith-audio.co.uk/code/dsp/html/classsignalsmith_1_1envelopes_1_1_peak_hold.html | CC-MAIN-2022-27 | refinedweb | 124 | 52.46 |
Aros/Developer/Games Programming/Basics
Contents
- 1 Introduction
- 2 AROS (Amiga)
- 3 2D
- 4 3D
- 5 2D texture onto 3D object
- 6 Collision
- 7 Pathfinding
- 8 Examples
Introduction[edit]
- learn to think like a programmer
- learn C
- learn how the AROS (Amiga) works
The first basically is about algorithm designs and things to avoid. Do you know what spaghetti code means? Structured programming? How about OO design? Big "O" notation? Recursion? Quick Sort? These are important concepts regardless of what language you use or platform you're on.
Simpler Language Introductions[edit]
C and company[edit]
Learning C isn't that hard, learning how to use it properly can be. The syntax for C although terse, is very simple. You could describe the entire C language on a couple of sheets of paper, there's little too it. However, like my prof always told me, C gives you enough rope to hang yourself (and everyone around you actually). Basically, C trusts that you know what you are doing and if you tell it to trash memory it will happily do it for you. C will not hold your hand like Basic, but it gives you more power and flexibility then just about any other language. Anyways, my best advice to anyone who's new with C is to study your pointers. And when you think you understand pointers, study them some more. That's the one part of C that gives people major headaches.
c value &c address of c *c pointed to by c
.c should contains functions .h usually contain #define #include typedef enum struct extern
C++ BASIC types and variables conditionals and loops i/o structures MEDIUM class constructor destructor methods instance variables
the underlying semantics of C++ ( e.g. when to use virtual, what a copy constructor does ) Even without data-hiding inheritance, references, polymorphism you have a powerful structure. Very handy features, such as function name overloading (used with care and sparingly), declarations as statements, references to name but a few... Data and methods put together called a class. OO language is classes & objects. OO means objects that have data and methods. Methods are sent from object to object and the object manipulates it's data. It has its share of problems too: the syntax is complex (although not unbearably so), it has no garbage collection and still has you managing memory by yourself, and quite a number of others, which may not directly affect a programmer working on his own, but will when working in a team.
Algorithms[edit]
Algorithms with youtube videos but start with small WB games first.
Algorithm theory involves thinking about the growth rates (Space and Time) and providing a breakdown of the issue into pseudo code and big O notation which taught what items to think about when choosing and optimizing algorithms
- search trees like: B tree, B+ tree, Red-black tree
- sorting algorithms like quicksort, natural merge sort, bucket bin sort,
- Breadth-first search (), Depth-first search (mazes),
- path finding like Hill Climb, A-star,
- Vectors,
Quicksort[edit]
# A is the array, p is the start position and r the end position # i is the pivot value, p the start position value and r the end position value # # Randomised-Partition(A,p,r) # i <- Random(p,r) # exchange A(r) with A(i) # return Partition(A,p,r) # # Randomised-QuickSort(A,p,r) # if p< r then # q <- Randomised-Partition(A,p,r) # Randomised-QuickSort(A,p,q) # Randomised-QuickSort(A,q+1,r) # # void quickSort(int numbers[], int array_size) { q_sort(numbers, 0, array_size - 1); } # choose (random?) pivot number and partition numbers into lower and greater around pivot void q_sort(int numbers[], int left, int right) { int pivot, l_hold, r_hold; l_hold = left; r_hold = right; pivot = numbers[left]; while (left < right) { while ((numbers[right] >= pivot) && (left < right)) right--; if (left != right) { numbers[left] = numbers[right]; left++; } while ((numbers[left] <= pivot) && (left < right)) left++; if (left != right) { numbers[right] = numbers[left]; right--; } } numbers[left] = pivot; pivot = left; left = l_hold; right = r_hold; if (left < pivot) q_sort(numbers, left, pivot-1); if (right > pivot) q_sort(numbers, pivot+1, right); }
Merge Sort[edit]; } }
AROS (Amiga)[edit]
Of course you need to learn programming on the Amiga. Lucky for you, the Amiga is a fun computer to program with a relatively small API. That is to say, you won't be swamped with OS calls, however, there are some ugly parts out there. If you want to just open a window and create some buttons, that's easy. Wanna write a web browser? That is gonna be hard and that is mostly because the OS doesn't provide a lot of the things you would need so you will end up writing it yourself. :-)
2D[edit]
- Setup Tiles, masking, platform stuff, etc
- Double buffering for moving objects sprites (collisions) or scrolling
- 2D engines which take out the hard work of writing your own routines (ike SDL)
- Make at least one type of game from each of the following board/grid, maze, card, etc for the experience
Rotations[edit]
/* assuming width and height are integers with the image's dimensions */ for(int x = 0; x < width; x++) { int hwidth = width / 2; int hheight = height / 2; double sinma = sin(-angle); double cosma = cos(-angle); for(int y = 0; y < height; y++) { int xt = x - hwidth; int yt = y - hheight; int xs = (int)round((cosma * xt - sinma * yt) + hwidth); int ys = (int)round((sinma * xt + cosma * yt) + hheight); if(xs >= 0 && xs < width && ys >= 0 && ys < height) { /* set target pixel (x,y) to color at (xs,ys) */ } else { /* set target pixel (x,y) to some default background */ } } }
Uses[edit]
2.5D Calculating Distance/Depth[edit]
A perspective transform (perspective projection == divide by Z) amounts to
x = x*d/z+d y = y*d/z+d
where d is the distance from the viewpoint and x, y, z are (obviously ) your x, y, z coordinates in 3d space If there is no "divide by Z", the depth-wise movement will feel wrong and it will feel like your object is accelerating/braking at the wrong times.
3d Projection
y_screen = (y_world / z) + (screen_height >> 1)
or:
z = y_world / (y_screen - (screen_height >> 1))
This formula takes the x or y world coordinates of an object, the z of the object, and returns the x or y pixel location. Or, alternately, given the world and screen coordinates, returns the z location.
Fast Linear Interpolation
o(x) = y1 + ((d * (y2-y1)) >> 16)
This assumes that all the numbers are in 16.16 fixed point. y1 and y2 are the two values to interpolate between, and d is the 16-bit fractional distance between the two points. For example, if d=$7fff, that would be halfway between the two values. This is useful for finding where between two segments a value is.
Fixed Point Arithmetic Floating point is very expensive for old systems which did not have specialized math hardware. Instead, a system called fixed point was used. This reserved a certain number of bits for the fractional part of the number. For a test case, say you only reserve one bit for the fractional amount, leaving seven bits for the whole number amounts. That fraction bit would represent one half (because a half plus a half equals a whole). To obtain the whole number value stored in that byte, the number is shifted right once. This can be expanded to use any number of bits for the fractional and whole portions of the number.
Fixed point multiplication.
Read more about 2.5D here
Maze Generation[edit]
Binary Tree (simple but has limitations) Sidewinder (better Binary tree) Depth First Search (DFS) (good simple mazes - traces route and backtracks to fill in missing) Growing Tree
Recursive Subdivision (wall adding - fractal like)
Aldous-Broeder (inefficient uniform spanning tree based) Wilson's (better spanning tree) Prim's (another spanning tree) Kruskal's (good but complex tree spanning)
Solving Algorithms
Dead-end retrace
a perfect maze, there is one and only one path from any point in the maze to any other point. That is, there are no inaccessible sections, no circular paths, and no open regions. A perfect maze can be generated easily with a computer using a depth first search algorithm.
A two dimensional maze can be represented as a rectangular array of square cells. Each cell has four walls. The state of each wall (north, south, east, and west) of each cell is maintained in a data structure consisting of an array of records. Each record stores a bit value that represents the state of each wall in a cell. To create a path between adjacent cells, the exit wall from the current cell and the entry wall to the next cell are removed. For example, if the next cell is to the right (east) of the current cell, remove the right (east) wall of the current cell and the left (west) wall of the next cell.
Depth-First Search - simplest maze generation algorithm
- Start at a random cell in the grid
- Look for a random neighbor cell you haven't been to yet
- If you find one, move there, knocking down the wall between the cells. If you don't find one, back up to the previous cell
- Repeat steps 2 and 3 until you've been to every cell in the grid
PSEUDOCODE
create a CellStack (LIFO) to hold a list of cell locations set TotalCells = number of cells in grid choose a cell at random and call it CurrentCell set VisitedCells = 1 while VisitedCells < TotalCells find all neighbors of CurrentCell with all walls intact if one or more found choose one at random knock down the wall between it and CurrentCell push CurrentCell location on the CellStack make the new cell CurrentCell add 1 to VisitedCells else pop the most recent cell entry off the CellStack make it CurrentCell endIf endWhile
assumed u have a x b size of maze, u need a + 1 and b + 1 of walls, so size of array should be (size * 2 + 1)
#include<stdio.h> #include<conio.h> #include<stdlib.h> #include<time.h> #define MAX 61 // 30 * 2 + 1 #define CELL 900 // 30 * 30 #define WALL 1 #define PATH 0 void init_maze(int maze[MAX][MAX]); void maze_generator(int indeks, int maze[MAX][MAX], int backtrack_x[CELL], int bactrack_y[CELL], int x, int y, int n, int visited); void print_maze(int maze[MAX][MAX], int maze_size); int is_closed(int maze[MAX][MAX], int x, int y); int main(void) { srand((unsigned)time(NULL)); int size; int indeks = 0; printf("MAZE CREATOR\n\n"); printf("input (0 ~ 30): "); scanf("%d", &size); printf("\n"); int maze[MAX][MAX]; int backtrack_x[CELL]; int backtrack_y[CELL]; init_maze(maze); backtrack_x[indeks] = 1; backtrack_y[indeks] = 1; maze_generator(indeks, maze, backtrack_x, backtrack_y, 1, 1, size, 1); print_maze(maze, size); getch(); return 0; } void init_maze(int maze[MAX][MAX]) { for(int a = 0; a < MAX; a++) { for(int b = 0; b < MAX; b++) { if(a % 2 == 0 || b % 2 == 0) maze[a][b] = 1; else maze[a][b] = PATH; } } } void maze_generator(int indeks, int maze[MAX][MAX], int backtrack_x[CELL], int backtrack_y[CELL], int x, int y, int n, int visited) { if(visited < n * n) { int neighbour_valid = -1; int neighbour_x[4]; int neighbour_y[4]; int step[4]; int x_next; int y_next; if(x - 2 > 0 && is_closed(maze, x - 2, y)) // upside { neighbour_valid++; neighbour_x[neighbour_valid]=x - 2;; neighbour_y[neighbour_valid]=y; step[neighbour_valid]=1; } if(y - 2 > 0 && is_closed(maze, x, y - 2)) // leftside { neighbour_valid++; neighbour_x[neighbour_valid]=x; neighbour_y[neighbour_valid]=y - 2; step[neighbour_valid]=2; } if(y + 2 < n * 2 + 1 && is_closed(maze, x, y + 2)) // rightside { neighbour_valid++; neighbour_x[neighbour_valid]=x; neighbour_y[neighbour_valid]=y + 2; step[neighbour_valid]=3; } if(x + 2 < n * 2 + 1 && is_closed(maze, x + 2, y)) // downside { neighbour_valid++; neighbour_x[neighbour_valid]=x+2; neighbour_y[neighbour_valid]=y; step[neighbour_valid]=4; } if(neighbour_valid == -1) { // backtrack x_next = backtrack_x[indeks]; y_next = backtrack_y[indeks]; indeks--; } if(neighbour_valid!=-1) { int randomization = neighbour_valid + 1; int random = rand()%randomization; x_next = neighbour_x[random]; y_next = neighbour_y[random]; indeks++; backtrack_x[indeks] = x_next; backtrack_y[indeks] = y_next; int rstep = step[random]; if(rstep == 1) maze[x_next+1][y_next] = PATH; else if(rstep == 2) maze[x_next][y_next + 1] = PATH; else if(rstep == 3) maze[x_next][y_next - 1] = PATH; else if(rstep == 4) maze[x_next - 1][y_next] = PATH; visited++; } maze_generator(indeks, maze, backtrack_x, backtrack_y, x_next, y_next, n, visited); } } void print_maze(int maze[MAX][MAX], int maze_size) { for(int a = 0; a < maze_size * 2 + 1; a++) { for(int b = 0; b < maze_size * 2 + 1; b++) { if(maze[a][b] == WALL) printf("#"); else printf(" "); } printf("\n"); } } int is_closed(int maze[MAX][MAX], int x, int y) { if(maze[x - 1][y] == WALL && maze[x][y - 1] == WALL && maze[x][y + 1] == WALL && maze[x + 1][y] == WALL ) return 1; return 0; }
Growing Tree
It starts by selecting a random cell and adding it to the list
x, y = rand(width), rand(height) cells << [x, y] The program them simply loops until the list is empty until cells.empty? # ... end
Within the loop, we first select the cell to operate on. I’m going to mask my own program’s complexity here behind a simple “choose_index” method; it takes a number and returns a number less than that.
index = choose_index(cells.length) x, y = cells[index]
Next, we iterate over a randomized list of directions, looking for an unvisited neighbor. If no such neighbor is found, we delete the given cell from the list before continuing.
[N, S, E, W].shuffle.each do |dir| nx, ny = x + DX[dir], y + DY[dir] if nx >= 0 && ny >= 0 && nx < width && ny < height && grid[ny][nx] == 0 # ... end end cells.delete_at(index) if index
When a valid, unvisited neighbor is located, we carve a passage between the current cell and that neighbor, add the neighbor to the list, set index to nil (to indicate that an unvisited neighbor was found), and then break out of the innermost loop.
grid[y][x] |= dir grid[ny][nx] |= OPPOSITE[dir] cells << [nx, ny] index = nil break
And that’s really all there is to it. Some possible implementations of the choose_index method might be:
def choose_index(ceil) return ceil-1 if choose_newest? return 0 if choose_oldest? return rand(ceil) if choose_random? # or implement your own! end
[edit]
3D[edit]
- solo route (hard and time consuming) ?? and use OpenGL (Mesa) routines]
- 3d graphics engine (need to add networking, physics, sound, scripting, level editor etc.) like Ogre3D C++, Crystal Space C++, irrlicht C++, 3D voxel etc, Cube C, Luxinia in C BSD, horde 3d, [], [ torque 3d],
- 3d game engines like Antiryad Gx, panda 3d, [Quake Doom id Tech 1 to 3 in C], [id Tech 4 in C plus plus], Urho3d, [Terathon C4 (Commercial),
2D texture onto 3D object[edit]
You need to create a separate context per class object instance and keep it alive as long as instance is alive. The context is bound to executing task and you can only have one context bound at a time. Opening the library itself does nothing - all actions are executed in relation to the context.
To get access to the right mouse button in an subclass I've added this in the setup method :
set(_win(obj), MUIA_Window_NoMenus, TRUE);
f the square you are drawing to is 2 dimensional and not rotated, you may be looking for glDrawPixels. It allows you to draw a rectangular region of pixels directly to the buffer without using any polygons.
glTexImage2D. This is the call that loads the image in OpenGL for a 2D Texture. glTexImage2D actually takes a raw pointer to the pixel data in the image. You can allocate memory yourself, and set the image data directly (however you want), then call this function to pass the image to OpenGL. Once you've created the texture, you can bind it to the state so that your triangles use that texture. If the texture needs to change, you will need to either re-do the glTexImage2D() call, or use something like glTexSubImage2D() to do a partial update.
just pass an array of GLubyte to the glTexImage2D function (as well as all the functions needed to bind the texture, etc). Haven't tried this exact snippet of code, but it should work fine. The array elements represent a serial version of the rows, columns and channels.
int pixelIndex = 0; GLubyte pixels[400]; for (int x = 0; x < 10; x++) { for (int y = 0; y < 10; x++) { for (int channel = 0; channel < 4; channel++) { // 0 = black, 255 = white pixels[pixelIndex++] = 255; } } } glTexImage2D( GL_TEXTURE_2D, 0, GL_RGBA, SIZE, SIZE, 0, GL_RGBA, GL_UNSIGNED_BYTE, pixels);
I've read in the OpenGL book you can use a 2D array for monochrome images, so I assume you could use a 3D array also.
Collision[edit]
Ray with Plane[edit]
- about a sphere intersecting triangles, and something called the "2PI summation method" to determine if a ray strikes a triangle.
- create a plane from your wall and do a ray to plane intersection test. A very simple test is a dot product test. If the result of the vector based scalar 'dot' product is >0, or the vectors are pointing in somewhat the same direction, then you know you are on the near side of the wall. If its <0, or the vectors are nearly pointing in the opposite directions then you are on the far side of the wall
- test for pixel perfect, you must find the point at which your camera ray intersected the plane in question. Back the camera up to that point, compute the collision response, and move on
- does a ray to triangle test and then computes the barycentric coords of the ray inside of the triangle. It will also bail on NAN's which can cause problems. It only uses dot products as well
The equation for intersection of ray and plane. This is easier to do in a maze because we know that all walls will form a plane so there is no need to do an expensive ray to triangle test.
Ray: p(t)=p0+td Plane: p dot n=d Equation: t=(d-p0 dot n)/(d dot n) If ray is parallel to plane or (d dot n)=0 then there is no intersection. If (d dot n)<0 then intersection during interval.
Solve for p0 which is actually p0.x and p0.y in this equation as well. This has been solved for t to test for intersection in this time interval. The nice thing about this is the dot product test and point test are rolled up in one algorithm. If the first time interval test passes, you can then solve for p0.
Pathfinding[edit]
- grid-based
- Djikstra's with tutorial and close cousin A* star and pseudocode
- flooding algorithm and then sound propagation. [ placing a virtual version of my character at a given position (usually a spawn point). I do an initial ray cast to place him flush against the ground and then add that single occupy-able cell to my "unprocessed list". I then check the four neighbors of that cell to see if a virtual player could step there with out being impeded/falling-climbing too much. I add the successful cells to the unprocessed list, and take my initial cell and put it in the processed list. repeat until the unprocessed list is empty.
The cells in my algorithm also store a position of the ground, and this can go up or down depending on if stairs or a ramp were encountered. When a sector is created from a list of related cells, it uses a axis aligned bounding box that encompass all these points (+ the width and height of each cell)]
- D* being a dynamic A*
- 3D mesh navigation
A star[edit]
A* (A star) algorithm moves through the grid from the given starting point to the given destination. Each "step" it makes it stores in a node. In this node data structure is stored three values
- the coordinates of the current block from the start
- the distance to the finish position from this block (different methods manhattan, diagonal, euclidian (optional squared version)
- and this block's parent block (for a later backtrack mode)
As the algorithm moves towards the destination, it stores these nodes into two stacks: the open and the closed stack. Once the destination block is reached, we go back through the nodes (using the pointer to the parent nodes) and we have our path described
Youtube video here and here
Insert the start point onto the open stack while( nodes left on open stack ) { //Pop first (closest) node off of open stack node = openstack.pop if( node.bDestination == 1 ) { Loop upwards through data structure to generate path exit function } //If we get here, this node isn't the destination for( up, down, forward, backward, left, right in grid ) { //GetNewNode returns null if block is occupied or in //closed stack newnode = GetNewNode( currentDirection ) if( newnode ) { //This InsertSorted function inserts the node //sorted based on the block's distance from the //destination openstack.InsertSorted(newnode); } } //Once a node is on the closedstack it is no longer used //(unless one of its children is the destination) closedstack.push( node ); }
In this algorithm the tricky part is actually in the InsertSorted() method of the openstack. You sort the nodes by their distance to the destination. This is the most important part of the algorithm, because the order in which the algorithm picks nodes to search is based on this sorting. Traditionally, (at least in the examples I've seen) you use the Manhattan Distance, which is the distance in grid blocks from the destination. I tweaked this distance function, and instead used the 3D distance of the centerpoint of the current block to the destination (using BlockDistance3D). For whatever reason this made the algorithm work better in my case...it consistantly searched less nodes than using the manhattan distance.
Examples[edit]
Minecraft clones OpenGL, Minetest C55, Theory, | http://en.wikibooks.org/wiki/Aros/Developer/Games_Programming/Basics | CC-MAIN-2014-10 | refinedweb | 3,662 | 54.46 |
ListBox Control
The ListBox control is used to show a list of strings which you can select. By default, you can only select one item. The List Box control is best used if you are trying to display a large number of items. The following are the commonly used properties of the ListBox control.
Figure 1 – ListBox Properties
The following are the useful methods you can use.
Figure 2 – ListBox Methods
To manipulate the items in the ListBox, we use the Items property which is of type ObjectCollection. You can use the typical collection methods such as Add, Remove, and Clear.
Create a new Windows Form and add a ListBox and a TextBox. Set the TextBox‘s Multiline property to true. Follow the layout shown below.
Name the ListBox listBoxInventory and the TextBox textBoxDescription. Double-click the form to add a Load event handler to it. Use the Form1_Load handler(line 16-29) of Example 1.
using System; using System.Collections.Generic; using System.Windows.Forms; namespace ListBoxDemo { public partial class Form1 : Form { private Dictionary<string, string> products; public Form1() { InitializeComponent(); } private void Form1_Load(object sender, EventArgs e) { products = new Dictionary<string, string>(); products.Add("Shampoo", "Makes your hair beautiful and shiny."); products.Add("Soap", "Removes the dirt and germs on your body."); products.Add("Deodorant", "Prevents body odor."); products.Add("Toothpaste", "Used to clean your teeth."); products.Add("Mouthwash", "Fights bad breath."); foreach (KeyValuePair<string, string> product in products) { listBoxInventory.Items.Add(product.Key); } } } }
Example 1
We created a Dictionary collection that has a string key, and a string value. Inside the Load event handler of the form, we added some products together with their description to this collection. Using a foreach loop, we add each product’s name to the ListBox‘s Items property. Not that each item in the generic Dictionary collection is of type KeyValuePari<TKey, TValue>. When you run the program, you will see that the five products can now be seen inside the ListBox. Note that if the height of the ListBox is insufficient to display all the items, then a vertical scrollbar will be visible to the right of the ListBox.
Now let’s add an event handler to the ListBox‘s SelectedIndexChanged event. The SelectedIndexChanged event occurs when the index of the selected item is changed. This is the default event of the ListBox so double clicking the ListBox will automatically add an event handler for the said event. Add this single line of code.
private void listBoxInventory_SelectedIndexChanged(object sender, EventArgs e) { textBoxDescription.Text = products[listBoxInventory.Text]; }
Now run the program and select a product. It’s corresponding description should display in the text box.
Please note that you can also use the String Collections Editor as shown in the last lesson to add items to the ListBox. | https://compitionpoint.com/listboxcontrol/ | CC-MAIN-2021-31 | refinedweb | 466 | 59.4 |
You can also run help( ) interactively (with no arguments):
>>> help() Welcome to Python 3.3! This is the interactive>
@alphaniner:
I'm sorry for not double checking, you are right, I forgot the usage of help() a bit:
help([object]).
Note this is from python 3.3
As you can see strings are the exception, but you can pass any other object to the help function, like this:
help([1,2,3,4,5]) help({'uno': 'one', 'dos': 'two'}) help({'aa', 'bb', 'cc'}) lucky = 777 help(lucky)
>>> class test: ... '''This is a test class.''' ... def test_method(): ... '''This does nothing!''' ... pass ... >>> help(test) Help on class test in module __main__: class test(builtins.object) | This is a test class. | | Methods defined here: | | test_method() | This does nothing! | | ------------------------------------------------------ | Data descriptors defined here: | | __dict__ | dictionary for instance variables (if defined) | | __weakref__ | list of weak references to the object (if defined) >>> test_instance = test() >>> help(test_instance) # The same as above
As you can see even user defined types can be used with help(), as long as you properly document your code with docstrings ('''docstring use triple quotes''')!
So I guess it's a matter of quoting the name of a string variable rather than its contents.
Try this:
Python 3.3.0 (v3.3.0:bd8afb90ebf2, Sep 29 2012, 10:55:48) [MSC v.1600 love this one:
In the face of ambiguity, refuse the temptation to guess.]]>
help('newname')
That didn't work in python 2 or 3:
>>> import fake >>> help('newname') no Python documentation found for 'newname'
However:
>>> help('fake.__name__')
Brought up a slightly 'customized' copy of help(str). So I guess it's a matter of quoting the name of a string variable rather than its contents.]]>
Indeed 'newname' is just a string assigned to the __name__ variable in your code, you can run some built-in functions like dir( ) to check the namespace, there is also globals( ) and locals( ). kaszak696 is right try passing 'newname' to help( ), notice the quotes that indicate it's a string:
help('newname')
as 'newname' is a string object you will get help for the string built-in type.]]>
That's because help doesn't care about the __name__, it only cares about the object it takes as an argument, and in your code the object 'newname' does not exist. If you want to import fakemodule under a name newname, you can do it like this:
import fakemodule as newname
If I manually declare __name__ in a module then import it, module.__name__ is my declared name, but help() only works if called with the default name. Just out of curiosity, I wonder what is the rationale behind this.
Edit: NVM. I overlooked the fact that I used fakemodule.__name__ (rather than newname.__name__ as I might have expected). So I guess __name__ has nothing to do with how the module or its contents are accessed.
fakemodule.py:
__name__ = 'newname'
python interpreter:
>>> import fakemodule >>>print(fakemodule.__name__) newname >>> help(newname) Traceback (most recent call last): File "<stdin>", line 1, in <module> NameError: name 'newname' is not defined >>> help(fakemodule)
help(fakemodule) output:
Help on module newname: NAME newname FILE /home/alphaniner/python3/fakemodule.py | https://bbs.archlinux.org/extern.php?action=feed&tid=160682&type=atom | CC-MAIN-2018-26 | refinedweb | 528 | 71.75 |
Hi,
I am experiencing missing “segments” in the output of imshow(). I draw a slowly growing line in an array, and then display it. The line is continuous but in the output, there are segments missing from it. Of course, if I zoom into the picture (before saving to output), then I can see the lines. However, if I save directly to a file then the segments are missing.
Here is a minimal example:
“”"
import numpy as np
import matplotlib.pyplot as plt
N = 600
slope = 15
x = np.zeros((N,N))
j = np.arange(N)
i = N/2 - j/slope
for idx in zip(i,j):
x[idx] = 1
plt.imshow(x, interpolation=‘nearest’, cmap=plt.cm.gray_r)
plt.savefig(‘bug.pdf’)
plt.savefig(‘bug.png’)
“”"
I have attached an example of the output. In theory, there should be a continuous line from the left side of the picture to the right side. The problem seems to occur across backends. Additionally, the thickness of the segments is not uniform. Some are thinner than the rest. Decreasing the value of N seems to make the issue go away. Increasing the value of N makes the problem worse.
Any ideas on what is going on and how I can fix it? | https://discourse.matplotlib.org/t/missing-segments-in-output-of-imshow/16557 | CC-MAIN-2022-21 | refinedweb | 210 | 69.38 |
Don't mind the mess!
We're currently in the process of migrating the Panda3D Manual to a new service. This is a temporary layout in the meantime.
Note: This article describes a deprecated feature as of Panda3D 1.10.0.
A package definition looks something like a Python class definition:
class mypackage(package): file('neededfile.dll') module('my.python.module') dir('/c/my/root_dir')
In fact, you can put any Python syntax you like into a pdef file, and it will be executed by ppackage. A pdef file is really just a special kind of Python program. The class syntax shown above is just the convention by which packages are declared.
The above sample generates a package called "mypackage", which contains the file neededfile.dll and the Python module my/python/module.py, as well as all files that those two files reference in turn; it also includes all of the contents of c:\my\root_dir .
More details of the pdef syntax will be provided soon. In the meantime, you can also examine the file direct/src/p3d/panda3d.pdef, for a sample file that produces the panda3d package itself (as well as some related packages).
You can also examine the file direct/src/p3d/Packager.py; any method of Packager named do_foo() produces a package function you can call named foo(). For instance, there is a Packager.do_file() method that accepts a Filename (as well as other optional parameters); this method is called when file() appears within a class definition in a pdef file.
Sometimes the files and modules you wish to include are not on the path, and thus can not be found. To see what is on the path is when your pdef file is run, you can use this at the top of your pdef file:
import sys print sys.path
Often when building packages, it's useful to have the working directory on the path, but it may be missing. It can be added with:
import sys sys.path.insert(0,'') #add the working directory as the first entry in sys.path
When making p3d packages, you use p3d instead of package for the class. An example p3d could be as follows:
import sys # add the working directory to the path so local files and modules can be found sys.path.insert(0,'') class MyP3D(p3d): require('morepy','panda3d','somePackage') # include some other packages config( version="0.0", display_name="MyP3D") module('core.*') # include the python package core, and its submodules dir('data',newDir='data') # include a folder called data mainModule('main') # include and set the main module that runs when the p3d is run file('events.txt') # include a text file
Generally what ppackage is pretty good about finding what modules are imported and automatically including them, but there are cases where this fails and explicitly specifying something like "module('api.*.*')" is useful.
As of Panda3D 1.7.1, you can specify an optional 'required' parameter to the file() or module() function call. By setting it to true, you can indicate that this file is vital to the package. Basically, when the file is missing and the required flag is set, it will refuse to build the package (rather than just emitting a warning).
You can put loops, if statements (based on os.name for example) and other flow control inside packages, but calling functions outside of them that add files and modules and such will not work.Previous Top Next | https://www.panda3d.org/manual/?title=The_pdef_syntax | CC-MAIN-2019-18 | refinedweb | 577 | 65.22 |
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Thread: import with ADO (Access 2000)
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import with ADO (Access 2000)
How to import all the forms from external database
I want to import all the forms available in an external database with the help of ADO. Actually,the same as when i select FileGetExternalDataSelectAllFormsImport. Otherwise i use the command Transferdtabase,but then i have to import each form separately.
Any help?
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Re: import with ADO (Access 2000)
Is there a reason you need to do this with code? DAO is easier for this purpose, but I can't think of a good reason not to do it from the UI instead ... unless you're trying to create a sort of database template.Charlotte
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Re: import with ADO (Access 2000)
Thank you for your reply.I need to do it with a code.Can i do it with DAO?Is it possible?I mean to import all the forms from
an external database without paying attention to their number ? Or it is not possible?
Thank you once again
regards
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Re: import with ADO (Access 2000)
It's possible either way. With DAO, forms are members of the Forms collection of the Database object. With ADO, they're members of the AllForms collection of the CurrentProject object. Here's a code routine (Access 2000 and higher only) that will import all the form object from another Access 2000 database into the current one, but be warned that this is not a fast process except on a very fast machine.
<pre>Function ImportAllForms(ByVal strDBName As String)
<font color=448800>'created by Charlotte Foust 9/23/2001 </font color=448800>
Dim appAccess As Access.Application
Dim frm As AccessObject
On Error GoTo Proc_err
<font color=448800> 'open a new instance of Access</font color=448800>
Set appAccess = New Access.Application
<font color=448800>'open the passed database name, not exclusive</font color=448800>
appAccess.OpenCurrentDatabase strDBName, False
<font color=448800>'Loop through the AllForms collection of the database</font color=448800>
For Each frm In appAccess.CurrentProject.AllForms
<font color=448800>'import each form into the current database</font color=448800>
DoCmd.TransferDatabase TransferType:=acImport, _
DatabaseType:="Microsoft Access", _
DatabaseName:=strDBName, _
ObjectType:=acForm, _
Source:=frm.name, _
Destination:=frm.name & "New"
Next frm <font color=448800>' In appAccess.CurrentProject.AllForms</font color=448800>
Proc_exit:
On Error Resume Next
<font color=448800>'cleanup and exit</font color=448800>
appAccess.CloseCurrentDatabase
Set appAccess = Nothing
Exit Function
Proc_err:
MsgBox Err.Number & "--" & Err.Description
Resume Proc_exit
End Function <font color=448800>'ImportAllForms(ByVal strDBName As String)</font color=448800></pre>
Charlotte | http://windowssecrets.com/forums/showthread.php/12632-import-with-ADO-%28Access-2000%29 | CC-MAIN-2017-09 | refinedweb | 496 | 55.34 |
Getting started with React and Contentful
The JavaScript library React is a popular tool to build interactive front end applications. Using the library, can deploy new React projects to any static hosting provider. This is great for performance and security, but also has a limitation: content often must be hardcoded in the application. To edit and update text or images, developers have to make code changes and redeploy the entire application.
Luckily, React handles API data very well. To make content editable, you can bring in an API-driven content management system (CMS) like Contentful. Contentful's content platform is an excellent choice to untangle content and code to offer content creators ways to edit data without the need for a source code deploy.
This guide to getting started with React explains how to connect a create-react-app application with Contentful's GraphQL API.
Prerequisite
To follow this tutorial, you need:
- a recent version of Node.js and npm available on your machine
- a free Contentful account
- a code editor
Create a new React application
The first thing is to bootstrap a new React application. Luckily, this use case is exactly why the
create-react-app npm package exists. Head over to your terminal and run the following commands:
npx create-react-app my-app cd my-app npm start # or yarn start
npx create-react-app creates and bootstraps a new React project. It comes with a recommended React toolchain, follows best practices and is ready for development. To learn more about the setup, read the official documentation.
npm start starts a local development server. It supports hot reloading and source code linting to make React development as straightforward as possible.
Compiled successfully! You can now view my-app in the browser. Local: On Your Network: Note that the development build is not optimized. To create a production build, use yarn build.
Open
localhost:3000 in your browser and find the
create-react-app default screen.
Your application is now ready to be developed. Let's change it to use Contentful API data.
Set up your Contentful space
Using Contentful, you can tailor content structures and the connected API responses to your needs. In this tutorial, you will use and fetch a "Page" entry that holds the information of a title and a logo to replace the hardcoded values included in
create-react-app.
In Contentful, create and open a new Contentful space. Then create a new
Page content type from the "Content model" section linked in the top navigation bar.
Ensure that the content type defines a
short text field for the title and a
one file media field to allow a file upload for the logo. Once you created the content type, you can create multiple entries with the defined structure that includes a title and a logo field.
Now, head to the "Content" section and create a new "Page" entry.
Fill the fields with your preferred data and publish the entry. You are now ready to fetch this entry from within the React application.
Fetch your content using GraphQL
To fetch the data stored in Contentful, you can use RESTful APIs (Content Deliver API, Content Management API and Content Preview API) or the GraphQL API.
This tutorial uses the GraphQL API. The main advantage of GraphQL is that developers can request and define the data included in the response. Additionally, GraphQL endpoints are self-documenting, and there is no need to install additional tooling or SDKs.
Explore Contentful's GraphQL endpoint using GraphiQL
To find out what data is available via the GraphQL endpoint, Contentful provides GraphiQL. GraphiQL is an in-browser tool that allows you to write GraphQL queries and explore the available data and schema.
We need to authenticate the made requests and provide an access token before we can use GraphiQL or the GraphQL API. Head to the API keys section in the Contentful UI (top-level navigation -> Settings -> API keys) and copy your Space ID and Content Delivery API access token.
With the Space ID and access token at hand, add these to the following URL and open GraphiQL in your browser:[YOUR_SPACE_ID]/explore?access_token=[YOUR_ACCESS_TOKEN]
access_tokenquery parameter or an
AuthorizationHTTP header.
Write your first GraphQL query
Now, use GraphiQL to write and define your GraphQL query. The tool allows you to make authenticated requests within its UI. Additionally, you can find the GraphQL schema documentation on the right side of the interface and you can write GraphQL queries with handy auto-completion.
Depending on your defined content model, the GraphQL API provides queryable fields. To query a single "Page" entry with an id, use
page(id), or query a collection of pages using the
pageCollection field.
For simplicity, this tutorial uses the queryable collection field. To fetch a collection of pages use the following query to retrieve the
title and
logo for every entry.
{ pageCollection { items { title logo { url } } } }
With this query you can move on and start fetching data from within the created React application.
Use Contentful GraphQL in your React application
The main component in your bootstrapped React application is
App.js. Let's edit the included functional component and bring in the Contentful data.
The provided component includes hardcorded data and has the following structure:
function App() { // let's fetch Contentful data!> ); }
Copy and paste the working GraphQL query into the file and define a new
query variable on top of the
App function.
const query = ` { pageCollection { items { title logo { url } } } } `
To make requests and connect functional React component to a particular state, add an import statement at the beginning of the file to import the React hooks
useState and
useEffect.
import {useState, useEffect} from "react";
Go into
App and define some initial state using
useState.
function App() { // define the initial state const [page, setPage] = useState(null); // show a loading screen case the data hasn't arrived yet if (!page) { return "Loading..."; } // return statement and JSX template. // ... }
useState allows you to define an initial state value. It returns the current value and a setter method for the specified data. Every time you call the returned setter (
setPage in this case) React rerenders the functional component.
At this stage, the React application always shows a loading message because you're not fetching any data yet. To retrieve the page entry stored in Contentful, use
useEffect to perform a request and set the returned data using
setPage.
window.fetchmethod provides all the functionality you need for this tutorial.
Define the URL endpoint ([YOUR_SPACE_ID]/) as the first function argument and pass in headers and additional configuration.
function App() { const [page, setPage] = useState(null); useEffect(() => { window .fetch(`[YOUR_SPACE_ID]/`, { method: "POST", headers: { "Content-Type": "application/json", // Authenticate the request Authorization: "Bearer [YOUR_ACCESS_TOKEN]", }, // send the GraphQL query body: JSON.stringify({ query }), }) .then((response) => response.json()) .then(({ data, errors }) => { if (errors) { console.error(errors); } // rerender the entire component with new data setPage(data.pageCollection.items[0]); }); }, []); if (!page) { return "Loading..."; } // return statement and JSX template. // ... }
useStateand
useEffectis not part of this tutorial. To learn more about this React functionality, read the official React documentation, or watch our GraphQL course's episode on the topic.
With the addition of
window.fetch called in
useEffect the
App component fetches GraphQL data from Contentful. But it is not rendering it yet. The last step is to update the returned JSX template to use the data. Change the logo URL and the hardcoded text to use
page.title and
page.logo.url.
The final state of your Contentful-connected React component now looks as follows:
import { useState, useEffect } from "react"; import "./App.css"; const query = ` { pageCollection { items { title logo { url } } } } `; function App() { const [page, setPage] = useState(null); useEffect(() => { window .fetch(`[YOUR_SPACE_ID]/`, { method: "POST", headers: { "Content-Type": "application/json", Authorization: "Bearer [YOUR_ACCESS_TOKEN]", }, body: JSON.stringify({ query }), }) .then((response) => response.json()) .then(({ data, errors }) => { if (errors) { console.error(errors); } setPage(data.pageCollection.items[0]); }); }, []); if (!page) { return "Loading..."; } // render the fetched Contentful data return ( <div className="App"> <header className="App-header"> <img src={page.logo.url} <p>{page.title}</p> </header> </div> ); } export default App;
Summary
In this tutorial, you learned how to create a new content type, how to create an entry of this type and fetch it from within a new React application using GraphQL. The application data is now editable from Contentful's UI, and you replaced the hardcoded React logo and message with dynamic API data.
Next steps
- Read the Contentful GraphQL API documentation
- Watch Contentful's GraphQL course
- Install the GraphQL playground app and use GraphQL tooling in the Contentful UI
Not what you’re looking for? Try our FAQ. | https://www.contentful.com/developers/docs/javascript/tutorials/getting-started-with-react-and-contentful/ | CC-MAIN-2021-10 | refinedweb | 1,435 | 56.05 |
Have you ever tried to change multiple values in a dataframe at once? We can do this very easily by replacing the values with another using a simple python code.
So this recipe is a short example on how to replace multiple values in a dataframe. Let's get started.
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import pandas as pd
import numpy as np
Here we have imported Pandas and Numpy which are very general libraries.
Let us create a simple dataset and convert it to a dataframe. This is a dataset of city with different features in it like City_level, City_pool, Rating, City_port and City_Temperature. We have converted this dataset into a dataframe with its features as columns.
city_data = {'city_level': [1, 3, 1, 2, 2, 3, 1, 1, 2, 3],
'city_pool' : ['y','y','n','y','n','n','y','n','n','y'],
'Rating': [1, 5, 3, 4, 1, 2, 3, 5, 3, 4],
'City_port': [0, 1, 0, 1, 0, 0, 1, 1, 0, 1],
'city_temperature': ['low', 'medium', 'medium', 'high', 'low','low', 'medium', 'medium', 'high', 'low']}
df = pd.DataFrame(city_data, columns = ['city_level', 'city_pool', 'Rating', 'City_port', 'city_temperature'])
So let us consider that first we want to print the initial dataset and then we want to replace digit 1 (where ever it is present in the dataset) with the string 'one'. Finally we want to view the new dataset with the changes.
So for this we have to use replace function which have 3 important parameters in it.
print(df)
df = df.replace(1, 'One')
print(); print(df)
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Once we run the above code snippet, we will see that the all the 1s in the dataset will be changed to 'one'.
city_level city_pool Rating City_port city_temperature 0 1 y 1 0 low 1 3 y 5 1 medium 2 1 n 3 0 medium 3 2 y 4 1 high 4 2 n 1 0 low 5 3 n 2 0 low 6 1 y 3 1 medium 7 1 n 5 1 medium 8 2 n 3 0 high 9 3 y 4 1 low city_level city_pool Rating City_port city_temperature 0 One y One 0 low 1 3 y 5 One medium 2 One n 3 0 medium 3 2 y 4 One high 4 2 n One 0 low 5 3 n 2 0 low 6 One y 3 One medium 7 One n 5 One medium 8 2 n 3 0 high 9 3 y 4 One low | https://www.projectpro.io/recipes/replace-multiple-values-in-pandas-dataframe | CC-MAIN-2021-43 | refinedweb | 437 | 70.36 |
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