autokluster

Auto-k spectral clustering for text embeddings with automatic cluster count estimation and quality metrics.

Why autokluster?

Traditional clustering algorithms like K-Means require you to specify the number of clusters k beforehand. This is problematic when you don't know how many natural groups exist in your data.

autokluster solves this by:

• Automatically estimating the optimal k using eigen-gap analysis
• Providing a Cohesion Ratio metric to assess clustering quality
• Being optimized for text embeddings from models like sentence-transformers

Installation

pip install autokluster

With sentence-transformers support:

pip install autokluster[embeddings]

Quick Start

from autokluster import cluster

# Your text embeddings (n_samples, n_features)
embeddings = ...

# Automatic clustering - k is found automatically
result = cluster(embeddings)

print(f"Found {result.k} clusters")           # e.g., 7
print(f"Cohesion Ratio: {result.cohesion_ratio:.2f}")  # e.g., 1.84 (>1 = good)
print(f"Labels: {result.labels}")             # [0, 2, 1, 0, 3, ...]

With fixed k

result = cluster(embeddings, k=5)  # Force 5 clusters

CLI

# Automatic k estimation
autokluster --input embeddings.npy --output clusters.json

# Fixed k
autokluster --input embeddings.npy --k 5

# Detailed output with eigenvalues
autokluster --input embeddings.npy --format detailed

How It Works

1. Spectral Clustering Pipeline

Embeddings → Cosine Similarity → Normalized Laplacian → Eigendecomposition → K-Means

2. Automatic k Estimation (Eigen-gap)

The algorithm analyzes gaps between consecutive eigenvalues of the Laplacian matrix. A significant gap indicates a natural cluster boundary:

δᵢ = |λᵢ - λᵢ₋₁| / moving_average(λ)
k = first i where δᵢ > threshold

3. Cohesion Ratio (ρ_C)

Measures clustering quality by comparing intra-cluster similarity to global similarity:

ρ_C = μ_intra / μ_global

• ρ_C = 1: Clusters are no more cohesive than random (bad)
• ρ_C > 1: Clusters are cohesive (good)
• ρ_C > 2: Highly cohesive clusters (excellent)

API Reference

cluster(embeddings, k=None, min_k=2, max_k=50, random_state=None)

ClusterResult

Requirements

• Python 3.10+
• numpy >= 1.24
• scipy >= 1.10
• scikit-learn >= 1.3

References

• Cohesion Ratio metric: arXiv:2511.19350
• Spectral clustering tutorial: von Luxburg (2007)

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

# Clone the repo
git clone https://github.com/FabienCadoret/autokluster.git
cd autokluster

# Install dev dependencies
pip install -e ".[dev]"

# Run tests
pytest tests/ -v

# Check linting
ruff check src/

License

MIT License - see LICENSE for details.