# sklearn.feature_selection.RFECV¶

class sklearn.feature_selection.RFECV(estimator, step=1, min_features_to_select=1, cv=None, scoring=None, verbose=0, n_jobs=None)[source]

Feature ranking with recursive feature elimination and cross-validated selection of the best number of features.

See glossary entry for cross-validation estimator.

Read more in the User Guide.

Parameters
estimatorobject

A supervised learning estimator with a fit method that provides information about feature importance either through a coef_ attribute or through a feature_importances_ attribute.

stepint or float, optional (default=1)

If greater than or equal to 1, then step corresponds to the (integer) number of features to remove at each iteration. If within (0.0, 1.0), then step corresponds to the percentage (rounded down) of features to remove at each iteration. Note that the last iteration may remove fewer than step features in order to reach min_features_to_select.

min_features_to_selectint, (default=1)

The minimum number of features to be selected. This number of features will always be scored, even if the difference between the original feature count and min_features_to_select isn’t divisible by step.

cvint, cross-validation generator or an iterable, optional

Determines the cross-validation splitting strategy. Possible inputs for cv are:

• None, to use the default 5-fold cross-validation,

• integer, to specify the number of folds.

• An iterable yielding (train, test) splits as arrays of indices.

For integer/None inputs, if y is binary or multiclass, sklearn.model_selection.StratifiedKFold is used. If the estimator is a classifier or if y is neither binary nor multiclass, sklearn.model_selection.KFold is used.

Refer User Guide for the various cross-validation strategies that can be used here.

Changed in version 0.22: cv default value of None changed from 3-fold to 5-fold.

scoringstring, callable or None, optional, (default=None)

A string (see model evaluation documentation) or a scorer callable object / function with signature scorer(estimator, X, y).

verboseint, (default=0)

Controls verbosity of output.

n_jobsint or None, optional (default=None)

Number of cores to run in parallel while fitting across folds. None means 1 unless in a joblib.parallel_backend context. -1 means using all processors. See Glossary for more details.

Attributes
n_features_int

The number of selected features with cross-validation.

support_array of shape [n_features]

The mask of selected features.

ranking_array of shape [n_features]

The feature ranking, such that ranking_[i] corresponds to the ranking position of the i-th feature. Selected (i.e., estimated best) features are assigned rank 1.

grid_scores_array of shape [n_subsets_of_features]

The cross-validation scores such that grid_scores_[i] corresponds to the CV score of the i-th subset of features.

estimator_object

The external estimator fit on the reduced dataset.

RFE

Recursive feature elimination

Notes

The size of grid_scores_ is equal to ceil((n_features - min_features_to_select) / step) + 1, where step is the number of features removed at each iteration.

Allows NaN/Inf in the input if the underlying estimator does as well.

References

R6f4d61ceb411-1

Guyon, I., Weston, J., Barnhill, S., & Vapnik, V., “Gene selection for cancer classification using support vector machines”, Mach. Learn., 46(1-3), 389–422, 2002.

Examples

The following example shows how to retrieve the a-priori not known 5 informative features in the Friedman #1 dataset.

>>> from sklearn.datasets import make_friedman1
>>> from sklearn.feature_selection import RFECV
>>> from sklearn.svm import SVR
>>> X, y = make_friedman1(n_samples=50, n_features=10, random_state=0)
>>> estimator = SVR(kernel="linear")
>>> selector = RFECV(estimator, step=1, cv=5)
>>> selector = selector.fit(X, y)
>>> selector.support_
array([ True,  True,  True,  True,  True, False, False, False, False,
False])
>>> selector.ranking_
array([1, 1, 1, 1, 1, 6, 4, 3, 2, 5])


Methods

 decision_function(self, X) Compute the decision function of X. fit(self, X, y[, groups]) Fit the RFE model and automatically tune the number of selected fit_transform(self, X[, y]) Fit to data, then transform it. get_params(self[, deep]) Get parameters for this estimator. get_support(self[, indices]) Get a mask, or integer index, of the features selected inverse_transform(self, X) Reverse the transformation operation predict(self, X) Reduce X to the selected features and then predict using the predict_log_proba(self, X) Predict class log-probabilities for X. predict_proba(self, X) Predict class probabilities for X. score(self, X, y) Reduce X to the selected features and then return the score of the set_params(self, \*\*params) Set the parameters of this estimator. transform(self, X) Reduce X to the selected features.
__init__(self, estimator, step=1, min_features_to_select=1, cv=None, scoring=None, verbose=0, n_jobs=None)[source]

Initialize self. See help(type(self)) for accurate signature.

decision_function(self, X)[source]

Compute the decision function of X.

Parameters
X{array-like or sparse matrix} of shape (n_samples, n_features)

The input samples. Internally, it will be converted to dtype=np.float32 and if a sparse matrix is provided to a sparse csr_matrix.

Returns
scorearray, shape = [n_samples, n_classes] or [n_samples]

The decision function of the input samples. The order of the classes corresponds to that in the attribute classes_. Regression and binary classification produce an array of shape [n_samples].

fit(self, X, y, groups=None)[source]
Fit the RFE model and automatically tune the number of selected

features.

Parameters
X{array-like, sparse matrix} of shape (n_samples, n_features)

Training vector, where n_samples is the number of samples and n_features is the total number of features.

yarray-like of shape (n_samples,)

Target values (integers for classification, real numbers for regression).

groupsarray-like of shape (n_samples,) or None

Group labels for the samples used while splitting the dataset into train/test set. Only used in conjunction with a “Group” cv instance (e.g., GroupKFold).

fit_transform(self, X, y=None, **fit_params)[source]

Fit to data, then transform it.

Fits transformer to X and y with optional parameters fit_params and returns a transformed version of X.

Parameters
Xnumpy array of shape [n_samples, n_features]

Training set.

ynumpy array of shape [n_samples]

Target values.

**fit_paramsdict

Returns
X_newnumpy array of shape [n_samples, n_features_new]

Transformed array.

get_params(self, 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
paramsmapping of string to any

Parameter names mapped to their values.

get_support(self, indices=False)[source]

Get a mask, or integer index, of the features selected

Parameters
indicesboolean (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. If indices is True, this is an integer array of shape [# output features] whose values are indices into the input feature vector.

inverse_transform(self, 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 by transform.

predict(self, X)[source]
Reduce X to the selected features and then predict using the

underlying estimator.

Parameters
Xarray of shape [n_samples, n_features]

The input samples.

Returns
yarray of shape [n_samples]

The predicted target values.

predict_log_proba(self, X)[source]

Predict class log-probabilities for X.

Parameters
Xarray of shape [n_samples, n_features]

The input samples.

Returns
parray of shape (n_samples, n_classes)

The class log-probabilities of the input samples. The order of the classes corresponds to that in the attribute classes_.

predict_proba(self, X)[source]

Predict class probabilities for X.

Parameters
X{array-like or sparse matrix} of shape (n_samples, n_features)

The input samples. Internally, it will be converted to dtype=np.float32 and if a sparse matrix is provided to a sparse csr_matrix.

Returns
parray of shape (n_samples, n_classes)

The class probabilities of the input samples. The order of the classes corresponds to that in the attribute classes_.

score(self, X, y)[source]
Reduce X to the selected features and then return the score of the

underlying estimator.

Parameters
Xarray of shape [n_samples, n_features]

The input samples.

yarray of shape [n_samples]

The target values.

set_params(self, **params)[source]

Set the parameters of this estimator.

The method works on simple estimators as well as on nested objects (such as pipelines). 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
selfobject

Estimator instance.

transform(self, X)[source]

Reduce X to the selected features.

Parameters
Xarray of shape [n_samples, n_features]

The input samples.

Returns
X_rarray of shape [n_samples, n_selected_features]

The input samples with only the selected features.