BERTopic/bertopic/representation/_langchain.py

import pandas as pd
from langchain.docstore.document import Document
from scipy.sparse import csr_matrix
from typing import Callable, Dict, Mapping, List, Tuple, Union

from bertopic.representation._base import BaseRepresentation
from bertopic.representation._utils import truncate_document

DEFAULT_PROMPT = "What are these documents about? Please give a single label."


class LangChain(BaseRepresentation):
    """ Using chains in langchain to generate topic labels.

    The classic example uses `langchain.chains.question_answering.load_qa_chain`.
    This returns a chain that takes a list of documents and a question as input.

    You can also use Runnables such as those composed using the LangChain Expression Language.

    Arguments:
        chain: The langchain chain or Runnable with a `batch` method.
               Input keys must be `input_documents` and `question`.
               Output key must be `output_text`.
        prompt: The prompt to be used in the model. If no prompt is given,
                `self.default_prompt_` is used instead.
        nr_docs: The number of documents to pass to LangChain if a prompt
                 with the `["DOCUMENTS"]` tag is used.
        diversity: The diversity of documents to pass to LangChain.
                   Accepts values between 0 and 1. A higher 
                   values results in passing more diverse documents
                   whereas lower values passes more similar documents.
        doc_length: The maximum length of each document. If a document is longer,
                    it will be truncated. If None, the entire document is passed.
        tokenizer: The tokenizer used to calculate to split the document into segments
                   used to count the length of a document. 
                       * If tokenizer is 'char', then the document is split up 
                         into characters which are counted to adhere to `doc_length`
                       * If tokenizer is 'whitespace', the document is split up
                         into words separated by whitespaces. These words are counted
                         and truncated depending on `doc_length`
                       * If tokenizer is 'vectorizer', then the internal CountVectorizer
                         is used to tokenize the document. These tokens are counted
                         and trunctated depending on `doc_length`. They are decoded with 
                         whitespaces.
                       * If tokenizer is a callable, then that callable is used to tokenize
                         the document. These tokens are counted and truncated depending
                         on `doc_length`
        chain_config: The configuration for the langchain chain. Can be used to set options
                      like max_concurrency to avoid rate limiting errors.
    Usage:

    To use this, you will need to install the langchain package first.
    Additionally, you will need an underlying LLM to support langchain,
    like openai:

    `pip install langchain`
    `pip install openai`

    Then, you can create your chain as follows:

    ```python
    from langchain.chains.question_answering import load_qa_chain
    from langchain.llms import OpenAI
    chain = load_qa_chain(OpenAI(temperature=0, openai_api_key=my_openai_api_key), chain_type="stuff")
    ```

    Finally, you can pass the chain to BERTopic as follows:

    ```python
    from bertopic.representation import LangChain

    # Create your representation model
    representation_model = LangChain(chain)

    # Use the representation model in BERTopic on top of the default pipeline
    topic_model = BERTopic(representation_model=representation_model)
    ```

    You can also use a custom prompt:

    ```python
    prompt = "What are these documents about? Please give a single label."
    representation_model = LangChain(chain, prompt=prompt)
    ```

    You can also use a Runnable instead of a chain.
    The example below uses the LangChain Expression Language:

    ```python
    from bertopic.representation import LangChain
    from langchain.chains.question_answering import load_qa_chain
    from langchain.chat_models import ChatAnthropic
    from langchain.schema.document import Document
    from langchain.schema.runnable import RunnablePassthrough
    from langchain_experimental.data_anonymizer.presidio import PresidioReversibleAnonymizer

    prompt = ...
    llm = ...

    # We will construct a special privacy-preserving chain using Microsoft Presidio

    pii_handler = PresidioReversibleAnonymizer(analyzed_fields=["PERSON"])

    chain = (
        {
            "input_documents": (
                lambda inp: [
                    Document(
                        page_content=pii_handler.anonymize(
                            d.page_content,
                            language="en",
                        ),
                    )
                    for d in inp["input_documents"]
                ]
            ),
            "question": RunnablePassthrough(),
        }
        | load_qa_chain(representation_llm, chain_type="stuff")
        | (lambda output: {"output_text": pii_handler.deanonymize(output["output_text"])})
    )

    representation_model = LangChain(chain, prompt=representation_prompt)
    ```
    """
    def __init__(self,
                 chain,
                 prompt: str = None,
                 nr_docs: int = 4,
                 diversity: float = None,
                 doc_length: int = None,
                 tokenizer: Union[str, Callable] = None,
                 chain_config = None,
                 ):
        self.chain = chain
        self.prompt = prompt if prompt is not None else DEFAULT_PROMPT
        self.default_prompt_ = DEFAULT_PROMPT
        self.chain_config = chain_config
        self.nr_docs = nr_docs
        self.diversity = diversity
        self.doc_length = doc_length
        self.tokenizer = tokenizer

    def extract_topics(self,
                       topic_model,
                       documents: pd.DataFrame,
                       c_tf_idf: csr_matrix,
                       topics: Mapping[str, List[Tuple[str, float]]]
                       ) -> Mapping[str, List[Tuple[str, int]]]:
        """ Extract topics

        Arguments:
            topic_model: A BERTopic model
            documents: All input documents
            c_tf_idf: The topic c-TF-IDF representation
            topics: The candidate topics as calculated with c-TF-IDF

        Returns:
            updated_topics: Updated topic representations
        """
        # Extract the top 4 representative documents per topic
        repr_docs_mappings, _, _, _ = topic_model._extract_representative_docs(
            c_tf_idf=c_tf_idf,
            documents=documents,
            topics=topics,
            nr_samples=500,
            nr_repr_docs=self.nr_docs,
            diversity=self.diversity
        )

        # Generate label using langchain's batch functionality
        chain_docs: List[List[Document]] = [
            [
                Document(
                    page_content=truncate_document(
                        topic_model,
                        self.doc_length,
                        self.tokenizer,
                        doc
                    )
                )
                for doc in docs
            ]
            for docs in repr_docs_mappings.values()
        ]

        # `self.chain` must take `input_documents` and `question` as input keys
        inputs = [
            {"input_documents": docs, "question": self.prompt}
            for docs in chain_docs
        ]

        # `self.chain` must return a dict with an `output_text` key
        # same output key as the `StuffDocumentsChain` returned by `load_qa_chain`
        outputs = self.chain.batch(inputs=inputs, config=self.chain_config)
        labels = [output["output_text"].strip() for output in outputs]

        updated_topics = {
            topic: [(label, 1)] + [("", 0) for _ in range(9)]
            for topic, label in zip(repr_docs_mappings.keys(), labels)
        }

        return updated_topics