langchain/chains/combine_documents/map_rerank.py

"""Combining documents by mapping a chain over them first, then reranking results."""

from __future__ import annotations

from typing import Any, Dict, List, Optional, Sequence, Tuple, Union, cast

from pydantic import BaseModel, Extra, root_validator

from langchain.chains.combine_documents.base import BaseCombineDocumentsChain
from langchain.chains.llm import LLMChain
from langchain.docstore.document import Document
from langchain.output_parsers.regex import RegexParser


class MapRerankDocumentsChain(BaseCombineDocumentsChain, BaseModel):
    """Combining documents by mapping a chain over them, then reranking results."""

    llm_chain: LLMChain
    """Chain to apply to each document individually."""
    document_variable_name: str
    """The variable name in the llm_chain to put the documents in.
    If only one variable in the llm_chain, this need not be provided."""
    rank_key: str
    """Key in output of llm_chain to rank on."""
    answer_key: str
    """Key in output of llm_chain to return as answer."""
    metadata_keys: Optional[List[str]] = None
    return_intermediate_steps: bool = False

    class Config:
        """Configuration for this pydantic object."""

        extra = Extra.forbid
        arbitrary_types_allowed = True

    @property
    def output_keys(self) -> List[str]:
        """Expect input key.

        :meta private:
        """
        _output_keys = super().output_keys
        if self.return_intermediate_steps:
            _output_keys = _output_keys + ["intermediate_steps"]
        if self.metadata_keys is not None:
            _output_keys += self.metadata_keys
        return _output_keys

    @root_validator()
    def validate_llm_output(cls, values: Dict) -> Dict:
        """Validate that the combine chain outputs a dictionary."""
        output_parser = values["llm_chain"].prompt.output_parser
        if not isinstance(output_parser, RegexParser):
            raise ValueError(
                "Output parser of llm_chain should be a RegexParser,"
                f" got {output_parser}"
            )
        output_keys = output_parser.output_keys
        if values["rank_key"] not in output_keys:
            raise ValueError(
                f"Got {values['rank_key']} as key to rank on, but did not find "
                f"it in the llm_chain output keys ({output_keys})"
            )
        if values["answer_key"] not in output_keys:
            raise ValueError(
                f"Got {values['answer_key']} as key to return, but did not find "
                f"it in the llm_chain output keys ({output_keys})"
            )
        return values

    @root_validator(pre=True)
    def get_default_document_variable_name(cls, values: Dict) -> Dict:
        """Get default document variable name, if not provided."""
        if "document_variable_name" not in values:
            llm_chain_variables = values["llm_chain"].prompt.input_variables
            if len(llm_chain_variables) == 1:
                values["document_variable_name"] = llm_chain_variables[0]
            else:
                raise ValueError(
                    "document_variable_name must be provided if there are "
                    "multiple llm_chain input_variables"
                )
        else:
            llm_chain_variables = values["llm_chain"].prompt.input_variables
            if values["document_variable_name"] not in llm_chain_variables:
                raise ValueError(
                    f"document_variable_name {values['document_variable_name']} was "
                    f"not found in llm_chain input_variables: {llm_chain_variables}"
                )
        return values

    def combine_docs(self, docs: List[Document], **kwargs: Any) -> Tuple[str, dict]:
        """Combine documents in a map rerank manner.

        Combine by mapping first chain over all documents, then reranking the results.
        """
        results = self.llm_chain.apply_and_parse(
            # FYI - this is parallelized and so it is fast.
            [{**{self.document_variable_name: d.page_content}, **kwargs} for d in docs]
        )
        return self._process_results(docs, results)

    async def acombine_docs(
        self, docs: List[Document], **kwargs: Any
    ) -> Tuple[str, dict]:
        """Combine documents in a map rerank manner.

        Combine by mapping first chain over all documents, then reranking the results.
        """
        results = await self.llm_chain.aapply_and_parse(
            # FYI - this is parallelized and so it is fast.
            [{**{self.document_variable_name: d.page_content}, **kwargs} for d in docs]
        )
        return self._process_results(docs, results)

    def _process_results(
        self,
        docs: List[Document],
        results: Sequence[Union[str, List[str], Dict[str, str]]],
    ) -> Tuple[str, dict]:
        typed_results = cast(List[dict], results)
        sorted_res = sorted(
            zip(typed_results, docs), key=lambda x: -int(x[0][self.rank_key])
        )
        output, document = sorted_res[0]
        extra_info = {}
        if self.metadata_keys is not None:
            for key in self.metadata_keys:
                extra_info[key] = document.metadata[key]
        if self.return_intermediate_steps:
            extra_info["intermediate_steps"] = results
        return output[self.answer_key], extra_info

    @property
    def _chain_type(self) -> str:
        return "map_rerank_documents_chain"