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Python implementations of metric learning algorithms

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Metric Learning algorithms in Python.


  • Large Margin Nearest Neighbor (LMNN)

  • Information Theoretic Metric Learning (ITML)

  • Sparse Determinant Metric Learning (SDML)

  • Least Squares Metric Learning (LSML)

  • Neighborhood Components Analysis (NCA)


  • Python 2.6+

  • numpy, scipy, scikit-learn

  • (for running the examples only: matplotlib)


Run python install for default installation.

Run python test to run all tests.


For full usage examples, see the test and examples directories.

Each metric is a subclass of BaseMetricLearner, which provides default implementations for the methods metric, transformer, and transform. Subclasses must provide an implementation for either metric or transformer.

For an instance of a metric learner named foo learning from a set of d-dimensional points, foo.metric() returns a d by d matrix M such that a distance between vectors x and y is expressed (x-y).dot(M).dot(x-y).

In the same scenario, foo.transformer() returns a d by d matrix L such that a vector x can be represented in the learned space as the vector

For convenience, the function foo.transform(X) is provided for converting a matrix of points (X) into the learned space, in which standard Euclidean distance can be used.


If a recent version of the Shogun Python modular (modshogun) library is available, the LMNN implementation will use the fast C++ version from there. The two implementations differ slightly, and the C++ version is more complete.


  • implement the rest of the methods on this site

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