Source code for langchain.retrievers.ensemble
"""
Ensemble retriever that ensemble the results of 
multiple retrievers by using weighted  Reciprocal Rank Fusion
"""
from typing import Any, Dict, List
from pydantic import root_validator
from langchain.callbacks.manager import (
    AsyncCallbackManagerForRetrieverRun,
    CallbackManagerForRetrieverRun,
)
from langchain.schema import BaseRetriever, Document
[docs]class EnsembleRetriever(BaseRetriever):
    """
    This class ensemble the results of multiple retrievers by using rank fusion.
    Args:
        retrievers: A list of retrievers to ensemble.
        weights: A list of weights corresponding to the retrievers. Defaults to equal
            weighting for all retrievers.
        c: A constant added to the rank, controlling the balance between the importance
            of high-ranked items and the consideration given to lower-ranked items.
            Default is 60.
    """
    retrievers: List[BaseRetriever]
    weights: List[float]
    c: int = 60
    @root_validator(pre=True)
    def set_weights(cls, values: Dict[str, Any]) -> Dict[str, Any]:
        if not values.get("weights"):
            n_retrievers = len(values["retrievers"])
            values["weights"] = [1 / n_retrievers] * n_retrievers
        return values
    def _get_relevant_documents(
        self,
        query: str,
        *,
        run_manager: CallbackManagerForRetrieverRun,
    ) -> List[Document]:
        """
        Get the relevant documents for a given query.
        Args:
            query: The query to search for.
        Returns:
            A list of reranked documents.