Overview

CohereRanker ranks Documents based on semantic relevance to a specified query. It uses Cohere rerank models for ranking. This list of all supported models can be found in Cohere’s documentation. The default model for this Ranker is rerank-english-v2.0.

You can also specify the top_k parameter to set the maximum number of Documents to return.

To start using this integration with Haystack, install it with:

pip install cohere-haystack

The component uses a COHERE_API_KEY or CO_API_KEY environment variable by default. Otherwise, you can pass a Cohere API key at initialization with api_key like this:

ranker = CohereRanker(api_key=Secret.from_token("<your-api-key>"))

Usage

On its own

This example uses CohereRanker to rank two simple documents. To run the Ranker, pass a query, provide the documents, and set the number of documents to return in the top_k parameter.

from haystack import Document
from haystack_integrations.components.rankers.cohere import CohereRanker

docs = [Document(content="Paris"), Document(content="Berlin")]

ranker = CohereRanker()

ranker.run(query="City in France", documents=docs, top_k=1)

In a Pipeline

Below is an example of a pipeline that retrieves documents from an InMemoryDocumentStore based on keyword search (using InMemoryBM25Retriever). It then uses the CohereRanker to rank the retrieved documents according to their similarity to the query. The pipeline uses the default settings of the Ranker.

from haystack import Document, Pipeline
from haystack.components.retrievers.in_memory import InMemoryBM25Retriever
from haystack.document_stores.in_memory import InMemoryDocumentStore
from haystack_integrations.components.rankers.cohere import CohereRanker

docs = [
    Document(content="Paris is in France"),
    Document(content="Berlin is in Germany"),
    Document(content="Lyon is in France"),
]
document_store = InMemoryDocumentStore()
document_store.write_documents(docs)

retriever = InMemoryBM25Retriever(document_store=document_store)
ranker = CohereRanker()

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 = "Cities in France"
res = document_ranker_pipeline.run(data={"retriever": {"query": query, "top_k": 3}, "ranker": {"query": query, "top_k": 2}})

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top_k parameter

In the example above, the top_k values for the Retriever and the Ranker are different. The Retriever's top_k specifies how many documents it returns. The Ranker then orders these documents.

You can set the same or a smaller top_k value for the Ranker. The Ranker's top_k is the number of documents it returns (if it's the last component in the pipeline) or forwards to the next component. In the pipeline example above, the Ranker is the last component, so the output you get when you run the pipeline are the top two documents, as per the Ranker's top_k.

Adjusting the top_k values can help you optimize performance. In this case, a smaller top_k value of the Retriever means fewer documents to process for the Ranker, which can speed up the pipeline.