sklearn.ensemble.VotingClassifier

class sklearn.ensemble.VotingClassifier(estimators, *, voting='hard', weights=None, n_jobs=None, flatten_transform=True, verbose=False)[source]

Soft Voting/Majority Rule classifier for unfitted estimators.

Read more in the User Guide.

New in version 0.17.

Parameters
estimatorslist of (str, estimator) tuples

Invoking the fit method on the VotingClassifier will fit clones of those original estimators that will be stored in the class attribute self.estimators_. An estimator can be set to 'drop' using set_params.

Changed in version 0.21: 'drop' is accepted. Using None was deprecated in 0.22 and support was removed in 0.24.

voting{‘hard’, ‘soft’}, default=’hard’

If ‘hard’, uses predicted class labels for majority rule voting. Else if ‘soft’, predicts the class label based on the argmax of the sums of the predicted probabilities, which is recommended for an ensemble of well-calibrated classifiers.

weightsarray-like of shape (n_classifiers,), default=None

Sequence of weights (float or int) to weight the occurrences of predicted class labels (hard voting) or class probabilities before averaging (soft voting). Uses uniform weights if None.

n_jobsint, default=None

The number of jobs to run in parallel for fit. None means 1 unless in a joblib.parallel_backend context. -1 means using all processors. See Glossary for more details.

New in version 0.18.

flatten_transformbool, default=True

Affects shape of transform output only when voting=’soft’ If voting=’soft’ and flatten_transform=True, transform method returns matrix with shape (n_samples, n_classifiers * n_classes). If flatten_transform=False, it returns (n_classifiers, n_samples, n_classes).

verbosebool, default=False

If True, the time elapsed while fitting will be printed as it is completed.

New in version 0.23.

Attributes
estimators_list of classifiers

The collection of fitted sub-estimators as defined in estimators that are not ‘drop’.

named_estimators_Bunch

Attribute to access any fitted sub-estimators by name.

New in version 0.20.

le_LabelEncoder

Transformer used to encode the labels during fit and decode during prediction.

classes_ndarray of shape (n_classes,)

The classes labels.

n_features_in_int

Number of features seen during fit.

feature_names_in_ndarray of shape (n_features_in_,)

Names of features seen during fit. Only defined if the underlying estimators expose such an attribute when fit. .. versionadded:: 1.0

See also

VotingRegressor

Prediction voting regressor.

Examples

>>> import numpy as np
>>> from sklearn.linear_model import LogisticRegression
>>> from sklearn.naive_bayes import GaussianNB
>>> from sklearn.ensemble import RandomForestClassifier, VotingClassifier
>>> clf1 = LogisticRegression(multi_class='multinomial', random_state=1)
>>> clf2 = RandomForestClassifier(n_estimators=50, random_state=1)
>>> clf3 = GaussianNB()
>>> X = np.array([[-1, -1], [-2, -1], [-3, -2], [1, 1], [2, 1], [3, 2]])
>>> y = np.array([1, 1, 1, 2, 2, 2])
>>> eclf1 = VotingClassifier(estimators=[
...         ('lr', clf1), ('rf', clf2), ('gnb', clf3)], voting='hard')
>>> eclf1 = eclf1.fit(X, y)
>>> print(eclf1.predict(X))
[1 1 1 2 2 2]
>>> np.array_equal(eclf1.named_estimators_.lr.predict(X),
...                eclf1.named_estimators_['lr'].predict(X))
True
>>> eclf2 = VotingClassifier(estimators=[
...         ('lr', clf1), ('rf', clf2), ('gnb', clf3)],
...         voting='soft')
>>> eclf2 = eclf2.fit(X, y)
>>> print(eclf2.predict(X))
[1 1 1 2 2 2]

To drop an estimator, set_params can be used to remove it. Here we dropped one of the estimators, resulting in 2 fitted estimators:

>>> eclf2 = eclf2.set_params(lr='drop')
>>> eclf2 = eclf2.fit(X, y)
>>> len(eclf2.estimators_)
2

Setting flatten_transform=True with voting='soft' flattens output shape of transform:

>>> eclf3 = VotingClassifier(estimators=[
...        ('lr', clf1), ('rf', clf2), ('gnb', clf3)],
...        voting='soft', weights=[2,1,1],
...        flatten_transform=True)
>>> eclf3 = eclf3.fit(X, y)
>>> print(eclf3.predict(X))
[1 1 1 2 2 2]
>>> print(eclf3.transform(X).shape)
(6, 6)

Methods

fit(X, y[, sample_weight])

Fit the estimators.

fit_transform(X[, y])

Return class labels or probabilities for each estimator.

get_feature_names_out([input_features])

Get output feature names for transformation.

get_params([deep])

Get the parameters of an estimator from the ensemble.

predict(X)

Predict class labels for X.

predict_proba(X)

Compute probabilities of possible outcomes for samples in X.

score(X, y[, sample_weight])

Return the mean accuracy on the given test data and labels.

set_params(**params)

Set the parameters of an estimator from the ensemble.

transform(X)

Return class labels or probabilities for X for each estimator.

fit(X, y, sample_weight=None)[source]

Fit the estimators.

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

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

yarray-like of shape (n_samples,)

Target values.

sample_weightarray-like of shape (n_samples,), default=None

Sample weights. If None, then samples are equally weighted. Note that this is supported only if all underlying estimators support sample weights.

New in version 0.18.

Returns
selfobject

Returns the instance itself.

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

Return class labels or probabilities for each estimator.

Return predictions for X for each estimator.

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

Input samples.

yndarray of shape (n_samples,), 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_feature_names_out(input_features=None)[source]

Get output feature names for transformation.

Parameters
input_featuresarray-like of str or None, default=None

Not used, present here for API consistency by convention.

Returns
feature_names_outndarray of str objects

Transformed feature names.

get_params(deep=True)[source]

Get the parameters of an estimator from the ensemble.

Returns the parameters given in the constructor as well as the estimators contained within the estimators parameter.

Parameters
deepbool, default=True

Setting it to True gets the various estimators and the parameters of the estimators as well.

Returns
paramsdict

Parameter and estimator names mapped to their values or parameter names mapped to their values.

property n_features_in_

Number of features seen during fit.

property named_estimators

Dictionary to access any fitted sub-estimators by name.

Returns
Bunch
predict(X)[source]

Predict class labels for X.

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

The input samples.

Returns
majarray-like of shape (n_samples,)

Predicted class labels.

predict_proba(X)[source]

Compute probabilities of possible outcomes for samples in X.

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

The input samples.

Returns
avgarray-like of shape (n_samples, n_classes)

Weighted average probability for each class per sample.

score(X, y, sample_weight=None)[source]

Return the mean accuracy on the given test data and labels.

In multi-label classification, this is the subset accuracy which is a harsh metric since you require for each sample that each label set be correctly predicted.

Parameters
Xarray-like of shape (n_samples, n_features)

Test samples.

yarray-like of shape (n_samples,) or (n_samples, n_outputs)

True labels for X.

sample_weightarray-like of shape (n_samples,), default=None

Sample weights.

Returns
scorefloat

Mean accuracy of self.predict(X) wrt. y.

set_params(**params)[source]

Set the parameters of an estimator from the ensemble.

Valid parameter keys can be listed with get_params(). Note that you can directly set the parameters of the estimators contained in estimators.

Parameters
**paramskeyword arguments

Specific parameters using e.g. set_params(parameter_name=new_value). In addition, to setting the parameters of the estimator, the individual estimator of the estimators can also be set, or can be removed by setting them to ‘drop’.

Returns
selfobject

Estimator instance.

transform(X)[source]

Return class labels or probabilities for X for each estimator.

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

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

Returns
probabilities_or_labels
If voting='soft' and flatten_transform=True:

returns ndarray of shape (n_samples, n_classifiers * n_classes), being class probabilities calculated by each classifier.

If voting='soft' and `flatten_transform=False:

ndarray of shape (n_classifiers, n_samples, n_classes)

If voting='hard':

ndarray of shape (n_samples, n_classifiers), being class labels predicted by each classifier.

Examples using sklearn.ensemble.VotingClassifier