A step-by-step Python tutorial on building a hybrid search system for RAG by combining BM25 lexical search with dense vector semantic search. The two independent retrieval engines are fused using Reciprocal Rank Fusion (RRF), which merges rankings rather than raw scores to produce a balanced final result. The guide covers installing rank_bm25 and sentence-transformers, implementing each search function, and applying RRF to merge results on a small sample dataset.
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