Source code for imblearn.over_sampling.random_over_sampler

"""Class to perform random over-sampling."""

# Authors: Guillaume Lemaitre <g.lemaitre58@gmail.com>
#          Christos Aridas
# License: MIT
from __future__ import division

from collections import Counter

import numpy as np
from sklearn.utils import check_random_state, safe_indexing

from .base import BaseOverSampler


[docs]class RandomOverSampler(BaseOverSampler): """Class to perform random over-sampling. Object to over-sample the minority class(es) by picking samples at random with replacement. Read more in the :ref:`User Guide <random_over_sampler>`. Parameters ---------- ratio : str, dict, or callable, optional (default='auto') Ratio to use for resampling the data set. - If ``str``, has to be one of: (i) ``'minority'``: resample the minority class; (ii) ``'majority'``: resample the majority class, (iii) ``'not minority'``: resample all classes apart of the minority class, (iv) ``'all'``: resample all classes, and (v) ``'auto'``: correspond to ``'all'`` with for over-sampling methods and ``'not minority'`` for under-sampling methods. The classes targeted will be over-sampled or under-sampled to achieve an equal number of sample with the majority or minority class. - If ``dict``, the keys correspond to the targeted classes. The values correspond to the desired number of samples. - If callable, function taking ``y`` and returns a ``dict``. The keys correspond to the targeted classes. The values correspond to the desired number of samples. random_state : int, RandomState instance or None, optional (default=None) If int, ``random_state`` is the seed used by the random number generator; If ``RandomState`` instance, random_state is the random number generator; If ``None``, the random number generator is the ``RandomState`` instance used by ``np.random``. Notes ----- Supports mutli-class resampling by sampling each class independently. See :ref:`sphx_glr_auto_examples_over-sampling_plot_comparison_over_sampling.py`, :ref:`sphx_glr_auto_examples_over-sampling_plot_random_over_sampling.py`, and :ref:`sphx_glr_auto_examples_applications_plot_over_sampling_benchmark_lfw.py`. Examples -------- >>> from collections import Counter >>> from sklearn.datasets import make_classification >>> from imblearn.over_sampling import \ RandomOverSampler # doctest: +NORMALIZE_WHITESPACE >>> X, y = make_classification(n_classes=2, class_sep=2, ... weights=[0.1, 0.9], n_informative=3, n_redundant=1, flip_y=0, ... n_features=20, n_clusters_per_class=1, n_samples=1000, random_state=10) >>> print('Original dataset shape {}'.format(Counter(y))) Original dataset shape Counter({1: 900, 0: 100}) >>> ros = RandomOverSampler(random_state=42) >>> X_res, y_res = ros.fit_sample(X, y) >>> print('Resampled dataset shape {}'.format(Counter(y_res))) Resampled dataset shape Counter({0: 900, 1: 900}) """
[docs] def __init__(self, ratio='auto', random_state=None): super(RandomOverSampler, self).__init__( ratio=ratio, random_state=random_state)
def _sample(self, X, y): """Resample the dataset. Parameters ---------- X : {array-like, sparse matrix}, shape (n_samples, n_features) Matrix containing the data which have to be sampled. y : array-like, shape (n_samples,) Corresponding label for each sample in X. Returns ------- X_resampled : {ndarray, sparse matrix}, shape \ (n_samples_new, n_features) The array containing the resampled data. y_resampled : ndarray, shape (n_samples_new,) The corresponding label of `X_resampled` """ random_state = check_random_state(self.random_state) target_stats = Counter(y) sample_indices = range(X.shape[0]) for class_sample, num_samples in self.ratio_.items(): target_class_indices = np.flatnonzero(y == class_sample) indices = random_state.randint( low=0, high=target_stats[class_sample], size=num_samples) sample_indices = np.append(sample_indices, target_class_indices[indices]) return (safe_indexing(X, sample_indices), safe_indexing(y, sample_indices))