Can Haystack be used for clustering and categorization of documents?

Haystack, an open-source framework for building search systems, is not specifically designed for clustering or categorization but can be adapted to support these tasks when combined with other tools. Its core strength lies in document retrieval and processing pipelines, which use embeddings (vector representations of text) to enable semantic search. While Haystack lacks built-in clustering algorithms or categorization models, developers can leverage its components—like embedding generation and integration with machine learning libraries—to create custom solutions for grouping or classifying documents.

For clustering, Haystack can generate document embeddings using its built-in retriever components (e.g., EmbeddingRetriever), which convert text into numerical vectors. These embeddings capture semantic similarities between documents, making them suitable for clustering algorithms like K-means or DBSCAN. For example, you could use Haystack to process a dataset of research papers, generate embeddings for each paper, and then apply scikit-learn’s clustering tools to group them by topic. This approach requires exporting embeddings from Haystack and using external libraries, but it simplifies the preprocessing and embedding steps, which are handled efficiently within Haystack pipelines.

For categorization, Haystack can integrate with classification models through custom nodes in its pipeline system. For instance, you could add a TransformersClassifier node to classify documents into predefined categories (e.g., labeling news articles as “sports,” “politics,” or “technology”). A typical workflow might involve retrieving documents with a retriever, passing them to a classifier, and filtering results based on predicted labels. While this requires training or fine-tuning a classifier separately, Haystack streamlines the pipeline setup and execution. However, it’s important to note that categorization in Haystack is less turnkey than its search capabilities—developers must implement classification logic themselves or rely on external model-serving tools.

In summary, Haystack’s flexibility allows it to serve as part of a larger system for clustering or categorization, but it doesn’t provide native implementations of these features. Its value lies in simplifying embedding generation, document processing, and pipeline orchestration, which can reduce the complexity of integrating with specialized machine learning libraries. Developers willing to combine Haystack with tools like scikit-learn, PyTorch, or Hugging Face models can build effective solutions, though this requires additional effort compared to using dedicated clustering or classification frameworks.