
Name	SentenceTransformersDiversityRanker
Folder path	/rankers/
Most common position in a pipeline	In a query pipeline, after a component that returns a list of documents (such as a Retriever)
Mandatory input variables	“query”: A search query string ”documents”: A list of documents to be ranked
Output variables	“documents”: A list of ranked documents

Overview

The SentenceTransformersDiversityRanker uses a ranking algorithm to order documents to maximize their overall diversity. It ranks a list of documents based on their similarity to the query. The component embeds the query and the documents using a pre-trained Sentence Transformers model.

This Ranker’s default model is sentence-transformers/all-MiniLM-L6-v2.

You can optionally set the top_k parameter, which specifies the maximum number of documents to return. If you don’t set this parameter, the component returns all documents it receives.

Find the full list of optional initialization parameters in our API reference.

Usage

On its own

from haystack import Document
from haystack.components.rankers import SentenceTransformersDiversityRanker

ranker = SentenceTransformersDiversityRanker(model="sentence-transformers/all-MiniLM-L6-v2", similarity="cosine")
ranker.warm_up()

docs = [Document(content="Regular Exercise"), Document(content="Balanced Nutrition"), Document(content="Positive Mindset"), 
        Document(content="Eating Well"), Document(content="Doing physical activities"), Document(content="Thinking positively")]
        
query = "How can I maintain physical fitness?"
output = ranker.run(query=query, documents=docs)
docs = output["documents"]

print(docs)

In a pipeline

from haystack import Document, Pipeline
from haystack.document_stores.in_memory import InMemoryDocumentStore
from haystack.components.retrievers.in_memory import InMemoryBM25Retriever
from haystack.components.rankers import SentenceTransformersDiversityRanker

docs = [Document(content="The iconic Eiffel Tower is a symbol of Paris"),
        Document(content="Visit Luxembourg Gardens for a haven of tranquility in Paris"),
        Document(content="The Pont Alexandre III bridge in Paris is famous for its Beaux-Arts style")]
document_store = InMemoryDocumentStore()
document_store.write_documents(docs)

retriever = InMemoryBM25Retriever(document_store = document_store)
ranker = SentenceTransformersDiversityRanker(meta_field="rating")

document_ranker_pipeline = Pipeline()
document_ranker_pipeline.add_component(instance=retriever, name="retriever")
document_ranker_pipeline.add_component(instance=ranker, name="ranker")

document_ranker_pipeline.connect("retriever.documents", "ranker.documents")

query = "Most famous iconic sight in Paris"
document_ranker_pipeline.run(data={"retriever": {"query": query, "top_k": 3}, 
                                   "ranker": {"query": query, "top_k": 2}})