Simple Fusion Retriever

In this example, we walk through how you can combine retireval results from multiple queries and multiple indexes.

The retrieved nodes will be returned as the top-k across all queries and indexes, as well as handling de-duplication of any nodes.

import os
import openai

os.environ["OPENAI_API_KEY"] = "sk-..."
openai.api_key = os.environ["OPENAI_API_KEY"]


For this notebook, we will use two very similar pages of our documentation, each stored in a separaete index.

from llama_index import SimpleDirectoryReader

documents_1 = SimpleDirectoryReader(
documents_2 = SimpleDirectoryReader(
from llama_index import VectorStoreIndex

index_1 = VectorStoreIndex.from_documents(documents_1)
index_2 = VectorStoreIndex.from_documents(documents_2)

Fuse the Indexes!

In this step, we fuse our indexes into a single retriever. This retriever will also generate augment our query by generating extra queries related to the original question, and aggregate the results.

This setup will query 4 times, once with your original query, and generate 3 more queries.

By default, it uses the following prompt to generate extra queries:

    "You are a helpful assistant that generates multiple search queries based on a "
    "single input query. Generate {num_queries} search queries, one on each line, "
    "related to the following input query:\n"
    "Query: {query}\n"
from llama_index.retrievers import QueryFusionRetriever

retriever = QueryFusionRetriever(
    [index_1.as_retriever(), index_2.as_retriever()],
    num_queries=4,  # set this to 1 to disable query generation
    # query_gen_prompt="...",  # we could override the query generation prompt here
# apply nested async to run in a notebook
import nest_asyncio

nodes_with_scores = retriever.retrieve("How do I setup a chroma vector store?")
Generated queries:
1. What are the steps to set up a chroma vector store?
2. Best practices for setting up a chroma vector store
3. Troubleshooting common issues when setting up a chroma vector store
for node in nodes_with_scores:
    print(f"Score: {node.score:.2f} - {node.text[:100]}...")
Score: 0.81 - construct vector store
neo4j_vector = Neo4jVectorStore(
Score: 0.80 - construct vector store
vector_store = ChromaVectorStore(

Use in a Query Engine!

Now, we can plug our retriever into a query engine to synthesize natural language responses.

from llama_index.query_engine import RetrieverQueryEngine

query_engine = RetrieverQueryEngine.from_args(retriever)
response = query_engine.query(
    "How do I setup a chroma vector store? Can you give an example?"
Generated queries:
1. How to set up a chroma vector store?
2. Step-by-step guide for creating a chroma vector store.
3. Examples of chroma vector store setups and configurations.
from llama_index.response.notebook_utils import display_response


Final Response: To set up a Chroma Vector Store, you can use the ChromaVectorStore class from the llama_index.vector_stores module. Here is an example of how to set it up:

from llama_index.vector_stores import ChromaVectorStore

# Assuming you have a chroma_collection variable
vector_store = ChromaVectorStore(

This code creates an instance of the ChromaVectorStore class, passing in the chroma_collection as a parameter.