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VectorStore
 Contents 
Maximum Marginal Relevance Retrieval
Similarity Score Threshold Retrieval
Specifying top k
VectorStore#
The index - and therefore the retriever - that LangChain has the most support for is the VectorStoreRetriever. As the name suggests, this retriever is backed heavily by a VectorStore.
Once you construct a VectorStore, its very easy to construct a retriever. Let’s walk through an example.
from langchain.document_loaders import TextLoader
loader = TextLoader('../../../state_of_the_union.txt')
from langchain.text_splitter import CharacterTextSplitter
from langchain.vectorstores import FAISS
from langchain.embeddings import OpenAIEmbeddings
documents = loader.load()
text_splitter = CharacterTextSplitter(chunk_size=1000, chunk_overlap=0)
texts = text_splitter.split_documents(documents)
embeddings = OpenAIEmbeddings()
db = FAISS.from_documents(texts, embeddings)
Exiting: Cleaning up .chroma directory
retriever = db.as_retriever()
docs = retriever.get_relevant_documents("what did he say about ketanji brown jackson")
Maximum Marginal Relevance Retrieval#
By default, the vectorstore retriever uses similarity search. If the underlying vectorstore support maximum marginal relevance search, you can specify that as the search type.
retriever = db.as_retriever(search_type="mmr")
docs = retriever.get_relevant_documents("what did he say abotu ketanji brown jackson")
Similarity Score Threshold Retrieval#
You can also use a retrieval method that sets a similarity score threshold and only returns documents with a score above that threshold
retriever = db.as_retriever(search_type="similarity_score_threshold", search_kwargs={"score_threshold": .5})
rtdocs_stable/api.python.langchain.com/en/stable/modules/indexes/retrievers/examples/vectorstore.html