.. _sphx_glr_auto_examples_under-sampling_plot_tomek_links.py:


===========
Tomek links
===========

An illustration of the Tomek links method.




.. image:: /auto_examples/under-sampling/images/sphx_glr_plot_tomek_links_001.png
    :align: center





.. code-block:: python


    # Authors: Andreas Mueller
    #          Christos Aridas
    #          Guillaume Lemaitre <g.lemaitre58@gmail.com>
    # License: MIT


    import numpy as np
    import matplotlib.pyplot as plt

    from sklearn.model_selection import train_test_split
    from sklearn.utils import shuffle

    from imblearn.under_sampling import TomekLinks

    print(__doc__)

    rng = np.random.RandomState(0)
    n_samples_1 = 500
    n_samples_2 = 50
    X_syn = np.r_[1.5 * rng.randn(n_samples_1, 2),
                  0.5 * rng.randn(n_samples_2, 2) + [2, 2]]
    y_syn = np.array([0] * (n_samples_1) + [1] * (n_samples_2))
    X_syn, y_syn = shuffle(X_syn, y_syn)
    X_syn_train, X_syn_test, y_syn_train, y_syn_test = train_test_split(X_syn,
                                                                        y_syn)

    # remove Tomek links
    tl = TomekLinks(return_indices=True)
    X_resampled, y_resampled, idx_resampled = tl.fit_sample(X_syn, y_syn)

    fig = plt.figure()
    ax = fig.add_subplot(1, 1, 1)

    idx_samples_removed = np.setdiff1d(np.arange(X_syn.shape[0]),
                                       idx_resampled)
    idx_class_0 = y_resampled == 0
    plt.scatter(X_resampled[idx_class_0, 0], X_resampled[idx_class_0, 1],
                alpha=.8, label='Class #0')
    plt.scatter(X_resampled[~idx_class_0, 0], X_resampled[~idx_class_0, 1],
                alpha=.8, label='Class #1')
    plt.scatter(X_syn[idx_samples_removed, 0], X_syn[idx_samples_removed, 1],
                alpha=.8, label='Removed samples')

    # make nice plotting
    ax.spines['top'].set_visible(False)
    ax.spines['right'].set_visible(False)
    ax.get_xaxis().tick_bottom()
    ax.get_yaxis().tick_left()
    ax.spines['left'].set_position(('outward', 10))
    ax.spines['bottom'].set_position(('outward', 10))
    ax.set_xlim([-5, 5])
    ax.set_ylim([-5, 5])
    plt.yticks(range(-5, 6))
    plt.xticks(range(-5, 6))

    plt.title('Under-sampling removing Tomek links')
    plt.legend()

    plt.show()

**Total running time of the script:** ( 0 minutes  0.130 seconds)



.. container:: sphx-glr-footer


  .. container:: sphx-glr-download

     :download:`Download Python source code: plot_tomek_links.py <plot_tomek_links.py>`



  .. container:: sphx-glr-download

     :download:`Download Jupyter notebook: plot_tomek_links.ipynb <plot_tomek_links.ipynb>`

.. rst-class:: sphx-glr-signature

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