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BM25

BM25 (Wikipedia) also known as the Okapi BM25, is a ranking function used in information retrieval systems to estimate the relevance of documents to a given search query.

BM25Retriever retriever uses the rank_bm25 package.

%pip install --upgrade --quiet  rank_bm25
from langchain_community.retrievers import BM25Retriever
API Reference:BM25Retriever

Create New Retriever with Texts​

retriever = BM25Retriever.from_texts(["foo", "bar", "world", "hello", "foo bar"])

Create a New Retriever with Documents​

You can now create a new retriever with the documents you created.

from langchain_core.documents import Document

retriever = BM25Retriever.from_documents(
    [
        Document(page_content="foo"),
        Document(page_content="bar"),
        Document(page_content="world"),
        Document(page_content="hello"),
        Document(page_content="foo bar"),
    ]
)
API Reference:Document

Use Retriever​

We can now use the retriever!

result = retriever.invoke("foo")
result
[Document(page_content='foo', metadata={}),
 Document(page_content='foo bar', metadata={}),
 Document(page_content='hello', metadata={}),
 Document(page_content='world', metadata={})]

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