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/// ------------------------------------------------------
/// SwarmOps - Numeric and heuristic optimization for C#
/// Copyright (C) 2003-2011 Magnus Erik Hvass Pedersen.
/// Please see the file license.txt for license details.
/// SwarmOps on the internet: http://www.Hvass-Labs.org/
/// ------------------------------------------------------
using System.Collections.Generic;
using System.Linq;
namespace SwarmOps.Extensions
{
/// <summary>
/// Various extensions to System-classes.
/// </summary>
public static partial class ExtensionMethods
{
/// <summary>
/// Computes the sum of squares of a sequence of System.Double values that
/// are obtained by invoking a transform function on each element of the
/// input sequence.
/// </summary>
/// <typeparam name="TSource">The type of the elements of source.</typeparam>
/// <param name="source">A sequence of values to calculate the sum of squares of.</param>
/// <param name="selector">A transform function to apply to each element.</param>
/// <returns>The sum of squares of the sequence of values.</returns>
public static double SumSquares<TSource>(this IEnumerable<TSource> source, System.Func<TSource, double> selector)
{
return source.Sum((elm) => { double x = selector(elm); return x * x; });
}
/// <summary>
/// Computes the standard deviation of a sequence of System.Double values that
/// are obtained by invoking a transform function on each element of the
/// input sequence.
/// </summary>
/// <typeparam name="TSource">The type of the elements of source.</typeparam>
/// <param name="source">A sequence of values to calculate the standard deviation of.</param>
/// <param name="selector">A transform function to apply to each element.</param>
/// <returns>The standard deviation of the sequence of values.</returns>
public static double StdDev<TSource>(this IEnumerable<TSource> source, System.Func<TSource, double> selector)
{
double sumSquares = source.SumSquares(selector);
double mean = source.Average(selector);
double stdDev = System.Math.Sqrt(sumSquares / source.Count() - mean * mean);
return stdDev;
}
}
}
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