FeatureRequest: MultiQueryRetriever should have the option to either do a union or intersection of the output

[ryanpeach]

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Feature request

Right now the retriever just gives you every result. Instead, give only the results that return for all queries.

Motivation

https://python.langchain.com/docs/modules/data_connection/retrievers/MultiQueryRetriever

For each query, it retrieves a set of relevant documents and takes the unique union across all queries to get a larger set of potentially relevant documents.

Proposal (If applicable)

A new flag called output_method which can have "union" or "intersection", and then do a set intersection before final return on all nodes which are common to the result of all queries.

[ryanpeach]

@karthik-sridhar-123 also requested this

[karthik-sridhar-123]

Yes, this is what I am planning on doing manually for now. This should really help in retrieving a fewer set of most relevant documents when we have a database of similar looking documents.