UMAP dimensionality reduction. Fast nonlinear manifold learning for 2D/3D visualization, clustering preprocessing (HDBSCAN), supervised/parametric UMAP, for high-dimensional data.
license
BSD-3-Clause license
metadata
{"skill-author":"K-Dense Inc."}
verified
false
lastVerifiedAt
"2026-02-19T05:29:09.098Z"
source
builtin
trust_score
100
provenance_sha
d4d2a49ce503943f
UMAP-Learn
Overview
UMAP (Uniform Manifold Approximation and Projection) is a dimensionality reduction technique for visualization and general non-linear dimensionality reduction. Apply this skill for fast, scalable embeddings that preserve local and global structure, supervised learning, and clustering preprocessing.
Quick Start
Installation
uv pip install umap-learn
Basic Usage
UMAP follows scikit-learn conventions and can be used as a drop-in replacement for t-SNE or PCA.
import umap
from sklearn.preprocessing import StandardScaler
# Prepare data (standardization is essential)
scaled_data = StandardScaler().fit_transform(data)
# Method 1: Single step (fit and transform)
embedding = umap.UMAP().fit_transform(scaled_data)
# Method 2: Separate steps (for reusing trained model)
reducer = umap.UMAP(random_state=42)
reducer.fit(scaled_data)
embedding = reducer.embedding_ # Access the trained embedding
Critical preprocessing requirement: Always standardize features to comparable scales before applying UMAP to ensure equal weighting across dimensions.
Custom metrics: User-defined distance functions via Numba
Recommendation: Use euclidean for numeric data, cosine for text/document vectors, hamming for binary data.
Parameter Tuning Example
# For visualization with emphasis on local structure
umap.UMAP(n_neighbors=15, min_dist=0.1, n_components=2, metric='euclidean')
# For clustering preprocessing
umap.UMAP(n_neighbors=30, min_dist=0.0, n_components=10, metric='euclidean')
# For document embeddings
umap.UMAP(n_neighbors=15, min_dist=0.1, n_components=2, metric='cosine')
# For preserving global structure
umap.UMAP(n_neighbors=100, min_dist=0.5, n_components=2, metric='euclidean')
Supervised and Semi-Supervised Dimension Reduction
UMAP supports incorporating label information to guide the embedding process, enabling class separation while preserving internal structure.
Supervised UMAP
Pass target labels via the y parameter when fitting:
When to use: When you have labeled data and want to separate known classes while keeping meaningful point embeddings.
Semi-Supervised UMAP
For partial labels, mark unlabeled points with -1 following scikit-learn convention:
# Create semi-supervised labels
semi_labels = labels.copy()
semi_labels[unlabeled_indices] = -1# Fit with partial labels
embedding = umap.UMAP().fit_transform(data, y=semi_labels)
When to use: When labeling is expensive or you have more data than labels available.
Metric Learning with UMAP
Train a supervised embedding on labeled data, then apply to new unlabeled data:
# Train on labeled data
mapper = umap.UMAP().fit(train_data, train_labels)
# Transform unlabeled test data
test_embedding = mapper.transform(test_data)
# Use as feature engineering for downstream classifierfrom sklearn.svm import SVC
clf = SVC().fit(mapper.embedding_, train_labels)
predictions = clf.predict(test_embedding)
When to use: For supervised feature engineering in machine learning pipelines.
UMAP for Clustering
UMAP serves as effective preprocessing for density-based clustering algorithms like HDBSCAN, overcoming the curse of dimensionality.
Best Practices for Clustering
Key principle: Configure UMAP differently for clustering than for visualization.
Recommended parameters:
n_neighbors: Increase to ~30 (default 15 is too local and can create artificial fine-grained clusters)
min_dist: Set to 0.0 (pack points densely within clusters for clearer boundaries)
n_components: Use 5-10 dimensions (maintains performance while improving density preservation vs. 2D)
# Create 2D embedding for visualization (separate from clustering)
vis_reducer = umap.UMAP(n_neighbors=15, min_dist=0.1, n_components=2, random_state=42)
vis_embedding = vis_reducer.fit_transform(scaled_data)
# Plot with cluster labelsimport matplotlib.pyplot as plt
plt.scatter(vis_embedding[:, 0], vis_embedding[:, 1], c=labels, cmap='Spectral', s=5)
plt.colorbar()
plt.title('UMAP Visualization with HDBSCAN Clusters')
plt.show()
Important caveat: UMAP does not completely preserve density and can create artificial cluster divisions. Always validate and explore resulting clusters.
Transforming New Data
UMAP enables preprocessing of new data through its transform() method, allowing trained models to project unseen data into the learned embedding space.
Basic Transform Usage
# Train on training data
trans = umap.UMAP(n_neighbors=15, random_state=42).fit(X_train)
# Transform test data
test_embedding = trans.transform(X_test)
Data consistency: The transform method assumes the overall distribution in the higher-dimensional space is consistent between training and test data. When this assumption fails, consider using Parametric UMAP instead.
Performance: Transform operations are efficient (typically <1 second), though initial calls may be slower due to Numba JIT compilation.
Scikit-learn compatibility: UMAP follows standard sklearn conventions and works seamlessly in pipelines:
Working with complex data types (images, sequences) benefiting from specialized architectures
When to use standard UMAP:
Need simplicity and quick prototyping
Dataset is small and computational efficiency isn't critical
Don't require learned transformations for future data
Inverse Transforms
Inverse transforms enable reconstruction of high-dimensional data from low-dimensional embeddings.
Basic usage:
reducer = umap.UMAP()
embedding = reducer.fit_transform(data)
# Reconstruct high-dimensional data from embedding coordinates
reconstructed = reducer.inverse_transform(embedding)
Important limitations:
Computationally expensive operation
Works poorly outside the convex hull of the embedding
Accuracy decreases in regions with gaps between clusters
Use cases:
Understanding structure of embedded data
Visualizing smooth transitions between clusters
Exploring interpolations between data points
Generating synthetic samples in embedding space
Example: Exploring embedding space:
import numpy as np
# Create grid of points in embedding space
x = np.linspace(embedding[:, 0].min(), embedding[:, 0].max(), 10)
y = np.linspace(embedding[:, 1].min(), embedding[:, 1].max(), 10)
xx, yy = np.meshgrid(x, y)
grid_points = np.c_[xx.ravel(), yy.ravel()]
# Reconstruct samples from grid
reconstructed_samples = reducer.inverse_transform(grid_points)
AlignedUMAP
For analyzing temporal or related datasets (e.g., time-series experiments, batch data):
from umap import AlignedUMAP
# List of related datasets
datasets = [day1_data, day2_data, day3_data]
# Create aligned embeddings
mapper = AlignedUMAP().fit(datasets)
aligned_embeddings = mapper.embeddings_ # List of embeddings
When to use: Comparing embeddings across related datasets while maintaining consistent coordinate systems.
Reproducibility
To ensure reproducible results, always set the random_state parameter:
reducer = umap.UMAP(random_state=42)
UMAP uses stochastic optimization, so results will vary slightly between runs without a fixed random state.
Common Issues and Solutions
Issue: Disconnected components or fragmented clusters
Solution: Increase n_neighbors to emphasize more global structure
Issue: Clusters too spread out or not well separated
Solution: Decrease min_dist to allow tighter packing
Issue: Poor clustering results
Solution: Use clustering-specific parameters (n_neighbors=30, min_dist=0.0, n_components=5-10)
Issue: Transform results differ significantly from training
Solution: Ensure test data distribution matches training, or use Parametric UMAP
Issue: Slow performance on large datasets
Solution: Set low_memory=True (default), or consider dimensionality reduction with PCA first
Issue: All points collapsed to single cluster
Solution: Check data preprocessing (ensure proper scaling), increase min_dist
Resources
references/
Contains detailed API documentation:
api_reference.md: Complete UMAP class parameters and methods
Load these references when detailed parameter information or advanced method usage is needed.
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