sklearn.feature_selection
.SelectKBest¶

class
sklearn.feature_selection.
SelectKBest
(score_func=<function f_classif>, *, k=10)[source]¶ Select features according to the k highest scores.
Read more in the User Guide.
 Parameters
 score_funccallable, default=f_classif
Function taking two arrays X and y, and returning a pair of arrays (scores, pvalues) or a single array with scores. Default is f_classif (see below “See Also”). The default function only works with classification tasks.
New in version 0.18.
 kint or “all”, default=10
Number of top features to select. The “all” option bypasses selection, for use in a parameter search.
 Attributes
 scores_arraylike of shape (n_features,)
Scores of features.
 pvalues_arraylike of shape (n_features,)
pvalues of feature scores, None if
score_func
returned only scores.
See also
f_classif
ANOVA Fvalue between label/feature for classification tasks.
mutual_info_classif
Mutual information for a discrete target.
chi2
Chisquared stats of nonnegative features for classification tasks.
f_regression
Fvalue between label/feature for regression tasks.
mutual_info_regression
Mutual information for a continuous target.
SelectPercentile
Select features based on percentile of the highest scores.
SelectFpr
Select features based on a false positive rate test.
SelectFdr
Select features based on an estimated false discovery rate.
SelectFwe
Select features based on familywise error rate.
GenericUnivariateSelect
Univariate feature selector with configurable mode.
Notes
Ties between features with equal scores will be broken in an unspecified way.
Examples
>>> from sklearn.datasets import load_digits >>> from sklearn.feature_selection import SelectKBest, chi2 >>> X, y = load_digits(return_X_y=True) >>> X.shape (1797, 64) >>> X_new = SelectKBest(chi2, k=20).fit_transform(X, y) >>> X_new.shape (1797, 20)
Methods
fit
(X, y)Run score function on (X, y) and get the appropriate features.
fit_transform
(X[, y])Fit to data, then transform it.
get_params
([deep])Get parameters for this estimator.
get_support
([indices])Get a mask, or integer index, of the features selected
Reverse the transformation operation
set_params
(**params)Set the parameters of this estimator.
transform
(X)Reduce X to the selected features.

fit
(X, y)[source]¶ Run score function on (X, y) and get the appropriate features.
 Parameters
 Xarraylike of shape (n_samples, n_features)
The training input samples.
 yarraylike of shape (n_samples,)
The target values (class labels in classification, real numbers in regression).
 Returns
 selfobject

fit_transform
(X, y=None, **fit_params)[source]¶ Fit to data, then transform it.
Fits transformer to
X
andy
with optional parametersfit_params
and returns a transformed version ofX
. Parameters
 Xarraylike of shape (n_samples, n_features)
Input samples.
 yarraylike of shape (n_samples,) or (n_samples, n_outputs), default=None
Target values (None for unsupervised transformations).
 **fit_paramsdict
Additional fit parameters.
 Returns
 X_newndarray array of shape (n_samples, n_features_new)
Transformed array.

get_params
(deep=True)[source]¶ Get parameters for this estimator.
 Parameters
 deepbool, default=True
If True, will return the parameters for this estimator and contained subobjects that are estimators.
 Returns
 paramsdict
Parameter names mapped to their values.

get_support
(indices=False)[source]¶ Get a mask, or integer index, of the features selected
 Parameters
 indicesbool, default=False
If True, the return value will be an array of integers, rather than a boolean mask.
 Returns
 supportarray
An index that selects the retained features from a feature vector. If
indices
is False, this is a boolean array of shape [# input features], in which an element is True iff its corresponding feature is selected for retention. Ifindices
is True, this is an integer array of shape [# output features] whose values are indices into the input feature vector.

inverse_transform
(X)[source]¶ Reverse the transformation operation
 Parameters
 Xarray of shape [n_samples, n_selected_features]
The input samples.
 Returns
 X_rarray of shape [n_samples, n_original_features]
X
with columns of zeros inserted where features would have been removed bytransform
.

set_params
(**params)[source]¶ Set the parameters of this estimator.
The method works on simple estimators as well as on nested objects (such as
Pipeline
). The latter have parameters of the form<component>__<parameter>
so that it’s possible to update each component of a nested object. Parameters
 **paramsdict
Estimator parameters.
 Returns
 selfestimator instance
Estimator instance.