/usr/lib/python3/dist-packages/sklearn/utils/class_weight.py is in python3-sklearn 0.17.0-4.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 | # Authors: Andreas Mueller
# Manoj Kumar
# License: BSD 3 clause
import warnings
import numpy as np
from ..externals import six
from ..utils.fixes import in1d
from .fixes import bincount
def compute_class_weight(class_weight, classes, y):
"""Estimate class weights for unbalanced datasets.
Parameters
----------
class_weight : dict, 'balanced' or None
If 'balanced', class weights will be given by
``n_samples / (n_classes * np.bincount(y))``.
If a dictionary is given, keys are classes and values
are corresponding class weights.
If None is given, the class weights will be uniform.
classes : ndarray
Array of the classes occurring in the data, as given by
``np.unique(y_org)`` with ``y_org`` the original class labels.
y : array-like, shape (n_samples,)
Array of original class labels per sample;
Returns
-------
class_weight_vect : ndarray, shape (n_classes,)
Array with class_weight_vect[i] the weight for i-th class
References
----------
The "balanced" heuristic is inspired by
Logistic Regression in Rare Events Data, King, Zen, 2001.
"""
# Import error caused by circular imports.
from ..preprocessing import LabelEncoder
if class_weight is None or len(class_weight) == 0:
# uniform class weights
weight = np.ones(classes.shape[0], dtype=np.float64, order='C')
elif class_weight in ['auto', 'balanced']:
# Find the weight of each class as present in y.
le = LabelEncoder()
y_ind = le.fit_transform(y)
if not all(np.in1d(classes, le.classes_)):
raise ValueError("classes should have valid labels that are in y")
# inversely proportional to the number of samples in the class
if class_weight == 'auto':
recip_freq = 1. / bincount(y_ind)
weight = recip_freq[le.transform(classes)] / np.mean(recip_freq)
warnings.warn("The class_weight='auto' heuristic is deprecated in"
" 0.17 in favor of a new heuristic "
"class_weight='balanced'. 'auto' will be removed in"
" 0.19", DeprecationWarning)
else:
recip_freq = len(y) / (len(le.classes_) *
bincount(y_ind).astype(np.float64))
weight = recip_freq[le.transform(classes)]
else:
# user-defined dictionary
weight = np.ones(classes.shape[0], dtype=np.float64, order='C')
if not isinstance(class_weight, dict):
raise ValueError("class_weight must be dict, 'auto', or None,"
" got: %r" % class_weight)
for c in class_weight:
i = np.searchsorted(classes, c)
if i >= len(classes) or classes[i] != c:
raise ValueError("Class label %d not present." % c)
else:
weight[i] = class_weight[c]
return weight
def compute_sample_weight(class_weight, y, indices=None):
"""Estimate sample weights by class for unbalanced datasets.
Parameters
----------
class_weight : dict, list of dicts, "balanced", or None, optional
Weights associated with classes in the form ``{class_label: weight}``.
If not given, all classes are supposed to have weight one. For
multi-output problems, a list of dicts can be provided in the same
order as the columns of y.
The "balanced" mode uses the values of y to automatically adjust
weights inversely proportional to class frequencies in the input data:
``n_samples / (n_classes * np.bincount(y))``.
For multi-output, the weights of each column of y will be multiplied.
y : array-like, shape = [n_samples] or [n_samples, n_outputs]
Array of original class labels per sample.
indices : array-like, shape (n_subsample,), or None
Array of indices to be used in a subsample. Can be of length less than
n_samples in the case of a subsample, or equal to n_samples in the
case of a bootstrap subsample with repeated indices. If None, the
sample weight will be calculated over the full sample. Only "auto" is
supported for class_weight if this is provided.
Returns
-------
sample_weight_vect : ndarray, shape (n_samples,)
Array with sample weights as applied to the original y
"""
y = np.atleast_1d(y)
if y.ndim == 1:
y = np.reshape(y, (-1, 1))
n_outputs = y.shape[1]
if isinstance(class_weight, six.string_types):
if class_weight not in ['balanced', 'auto']:
raise ValueError('The only valid preset for class_weight is '
'"balanced". Given "%s".' % class_weight)
elif (indices is not None and
not isinstance(class_weight, six.string_types)):
raise ValueError('The only valid class_weight for subsampling is '
'"balanced". Given "%s".' % class_weight)
elif n_outputs > 1:
if (not hasattr(class_weight, "__iter__") or
isinstance(class_weight, dict)):
raise ValueError("For multi-output, class_weight should be a "
"list of dicts, or a valid string.")
if len(class_weight) != n_outputs:
raise ValueError("For multi-output, number of elements in "
"class_weight should match number of outputs.")
expanded_class_weight = []
for k in range(n_outputs):
y_full = y[:, k]
classes_full = np.unique(y_full)
classes_missing = None
if class_weight in ['balanced', 'auto'] or n_outputs == 1:
class_weight_k = class_weight
else:
class_weight_k = class_weight[k]
if indices is not None:
# Get class weights for the subsample, covering all classes in
# case some labels that were present in the original data are
# missing from the sample.
y_subsample = y[indices, k]
classes_subsample = np.unique(y_subsample)
weight_k = np.choose(np.searchsorted(classes_subsample,
classes_full),
compute_class_weight(class_weight_k,
classes_subsample,
y_subsample),
mode='clip')
classes_missing = set(classes_full) - set(classes_subsample)
else:
weight_k = compute_class_weight(class_weight_k,
classes_full,
y_full)
weight_k = weight_k[np.searchsorted(classes_full, y_full)]
if classes_missing:
# Make missing classes' weight zero
weight_k[in1d(y_full, list(classes_missing))] = 0.
expanded_class_weight.append(weight_k)
expanded_class_weight = np.prod(expanded_class_weight,
axis=0,
dtype=np.float64)
return expanded_class_weight
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