DBGSOM

DBGSOM (Directed Batch Growing Self-Organizing Map): A Neural Network for Clustering, Classification, Nonlinear Projection/Manifold learning, Data Visualization.

The network automatically determines the number of prototypes needed to represent the data. Starting from 4 neurons, the map expands at boundary positions where quantization error exceeds a configurable threshold: no need to pre-specify cluster count. The result is a topology-preserving 2D grid where neighboring neurons represent similar inputs.

Features

• No cluster count needed — map grows until quantization error falls below threshold; lambda_ controls sensitivity
• sklearn-compatible — drop-in for KMeans, DBSCAN: implements fit_predict, transform, score, and predict_proba
• Topology-preserving — related samples cluster as grid neighbors; topographic error < 5% on Digits
• Faster than classical SOMs — batch learning rule trains on all samples per epoch (vs. online, sample-by-sample)
• Built-in visualization — plot() renders neuron grid coloured by density, label, error or hit count.

How it works

In brief: Four neurons initialize → samples assigned to nearest neuron → weights update toward assigned samples → boundary neurons with high error spawn new neighbors → σ decays → repeat until max_neurons or n_iter reached. Neighboring neurons influence each other's weight update → topology preserved during training.

DBGSOM builds a 2D rectangular prototype map where each neuron connects to four neighbors. Four neurons init with random weights from input data. Each epoch: every sample is assigned to the nearest neuron (BMU); weights are updated toward mean of the mapped samples. A neighborhood function couples neighboring neurons so that low-dimensional map ordering is preserved; neighborhood width shrinks over time (global → local structure). A growing mechanism inserts new neurons at boundary positions where quantization error exceeds growing threshold.

How to install

Download from PyPI

Install from PyPI via uv (recommended):

uv add dbgsom

or with pip:

pip install dbgsom

Install from source

Clone and install with uv (recommended):

git clone https://github.com/SandroMartens/DBGSOM.git
cd DBGSOM
uv sync

Alternatively with pip:

git clone https://github.com/SandroMartens/DBGSOM.git
cd DBGSOM
pip install -e .

Usage

DBGSOM implements the scikit-learn API and provides two estimators:

Class	Use case
SomVQ	Unsupervised clustering / vector quantization
SomClassifier	Supervised classification

Clustering / Vector Quantization

from dbgsom import SomVQ
from sklearn.datasets import load_digits

X, y = load_digits(return_X_y=True)

vq = SomVQ(lambda_=80.0, max_neurons=80)
labels = vq.fit_predict(X)

print(f"Neurons: {len(vq.neurons_)}")
print(f"Quantization error: {vq.quantization_error_:.4f}")
print(f"Topographic error:  {vq.topographic_error_:.4f}")

Key growth parameters:

Parameter	Default	Effect
lambda_	115.0	Growing threshold — higher → fewer neurons
max_neurons	5 x sqrt(n_samples)	Hard cap on neuron count
n_iter	500	Training epochs; growth only happens in first half

Classification

from dbgsom import SomClassifier
from sklearn.datasets import load_digits
from sklearn.model_selection import train_test_split

X, y = load_digits(return_X_y=True)
X_train, X_test, y_train, y_test = train_test_split(X, y, random_state=42)

clf = SomClassifier(lambda_=80.0, max_neurons=80)
clf.fit(X_train, y_train)

print(clf.score(X_test, y_test))           # accuracy
proba = clf.predict_proba(X_test)          # class probabilities

Transform

Both estimators implement transform() — represents each sample as sparse non-negative linear combination of prototype weights:

coefs = vq.transform(X)   # shape (n_samples, n_prototypes)

Visualization

plot() renders SOM neurons as dots and neighborhood edges as grey lines via seaborn objects.

vq.plot(color="density")                       # continuous -> colour gradient
clf.plot(color="label")                        # categorical -> colour legend
vq.plot(color="hit_count", pointsize="error")  # colour + size encoding
vq.plot(color="density", layout="pca", palette="magma_r")

Supported attributes for color / pointsize: 'label', 'epoch_created', 'error', 'average_distance', 'density', 'hit_count'

Parameter	Options	Description
color	any node attribute	Numeric attributes → continuous colour scale; int/str with ≤ 20 unique values → legend
pointsize	any numeric attribute	Node size proportional to attribute value
layout	'grid' (default), 'pca'	Node placement algorithm
palette	any Matplotlib colormap	Applied to colour mapping

Examples

Example	Description
	2D input: prototypes (red) approximate input distribution (white), square topology preserved.
	Fashion-MNIST: weight of each prototype plotted; neighboring prototypes pairwise similar.
	Each prototype coloured by majority class; same-class samples cluster together. Trained on MNIST digits.

Comparisons

SOM algorithm comparison (Digits, PCA projection)

DBGSOM (dynamic grid, size determined automatically) vs. MiniSom and SuSi (fixed grids) vs. KMeans (no topology). All trained on same Digits embedding.

Clustering metrics (Digits dataset)

ARI, Silhouette, Davies-Bouldin, training time. All algorithms use same cluster count — determined automatically by DBGSOM.

Full benchmark notebooks:

Notebook	What it shows
clustering_comparison.ipynb	DBGSOM vs. KMeans, MiniBatchKMeans, AgglomerativeClustering on Iris and Digits
som_comparison.ipynb	DBGSOM vs. MiniSom, SuSi on Digits and Fashion-MNIST (QE, TE, training time, scaling)
manifold_comparison.ipynb	DBGSOM vs. Isomap, t-SNE, UMAP on MNIST: trustworthiness, continuity, folds/tears, runtime

Dependencies

• Python >= 3.12
• numpy
• numba
• NetworkX
• tqdm
• scikit-learn
• seaborn
• pandas

Citation

If you use DBGSOM in your research, please cite:

Martens, S. (2025). DBGSOM: A Python implementation of the Directed Batch Growing Self-Organizing Map. Zenodo. https://doi.org/10.5281/zenodo.20525611

References

• A directed batch growing approach to enhance the topology preservation of self-organizing map, Mahdi Vasighi and Homa Amini, 2017, http://dx.doi.org/10.1016/j.asoc.2017.02.015
• Reference implementation by the authors in Matlab: https://github.com/mvasighi/DBGSOM
• Statistics-enhanced Direct Batch Growth Self-Organizing Mapping for efficient DoS Attack Detection, Xiaofei Qu et al., 2019, 10.1109/ACCESS.2019.2922737
• Entropy-Defined Direct Batch Growing Hierarchical Self-Organizing Mapping for Efficient Network Anomaly Detection, Xiaofei Qu et al., 2021, 10.1109/ACCESS.2021.3064200
• Self-Organizing Maps, 3rd Edition, Teuvo Kohonen, 2003
• MATLAB Implementations and Applications of the Self-Organizing Map, Teuvo Kohonen, 2014
• Smoothed self-organizing map for robust clustering, P. D'Urso, L. De Giovanni and R. Massari, 2019, https://doi.org/10.1016/j.ins.2019.06.038

License

dbgsom is licensed under MIT license.