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What are Sparse Vectors?

Sparse vectors are high-dimensional vectors with mostly zero values, designed for keyword-based retrieval. Unlike dense embeddings which capture semantic meaning, sparse vectors excel at:
  • Exact keyword matching: Finding documents containing specific terms
  • Domain-specific terminology: Better at matching technical terms, proper nouns, and rare words
  • Lexical retrieval: BM25-style retrieval patterns
Sparse vectors use models like SPLADE that assign importance weights to specific tokens, making them complementary to dense semantic embeddings.

Enabling Sparse Vector Index

To use sparse vectors, add a sparse vector index to your schema. The key parameter is the metadata field name where sparse embeddings will be stored - you can name it whatever you want:

Create Collection and Add Data

Create Collection with Schema

Add Data

When you add documents, sparse embeddings are automatically generated from the source key:
Once configured, you can search using sparse vectors alone or combine them with dense embeddings for hybrid search. Use sparse vectors for keyword-based retrieval:
Hybrid search combines dense semantic embeddings with sparse keyword embeddings for improved retrieval quality. By merging results from both approaches using Reciprocal Rank Fusion (RRF), you often achieve better results than either approach alone.
  • Semantic + Lexical: Dense embeddings capture meaning while sparse vectors catch exact keywords
  • Improved recall: Finds relevant documents that either semantic or keyword search might miss alone
  • Balanced results: Combines the strengths of both retrieval methods

Combining Dense and Sparse with RRF

Use RRF (Reciprocal Rank Fusion) to merge dense and sparse search results:

Next Steps