"""
Soft Voting/Majority Rule classifier.
This module contains a Soft Voting/Majority Rule classifier for
classification estimators.
"""
# Authors: Sebastian Raschka <se.raschka@gmail.com>,
# Gilles Louppe <g.louppe@gmail.com>
#
# License: BSD 3 clause
import numpy as np
import warnings
from ..base import ClassifierMixin
from ..base import TransformerMixin
from ..base import clone
from ..preprocessing import LabelEncoder
from ..externals.joblib import Parallel, delayed
from ..utils.validation import has_fit_parameter, check_is_fitted
from ..utils.metaestimators import _BaseComposition
def _parallel_fit_estimator(estimator, X, y, sample_weight=None):
"""Private function used to fit an estimator within a job."""
if sample_weight is not None:
estimator.fit(X, y, sample_weight=sample_weight)
else:
estimator.fit(X, y)
return estimator
class VotingClassifier(_BaseComposition, ClassifierMixin, TransformerMixin):
"""Soft Voting/Majority Rule classifier for unfitted estimators.
.. versionadded:: 0.17
Read more in the :ref:`User Guide <voting_classifier>`.
Parameters
----------
estimators : list of (string, 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 `None` using
``set_params``.
voting : str, {'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.
weights : array-like, shape = [n_classifiers], optional (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_jobs : int, optional (default=1)
The number of jobs to run in parallel for ``fit``.
If -1, then the number of jobs is set to the number of cores.
flatten_transform : bool, optional (default=None)
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).
Attributes
----------
estimators_ : list of classifiers
The collection of fitted sub-estimators as defined in ``estimators``
that are not `None`.
classes_ : array-like, shape = [n_predictions]
The classes labels.
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(random_state=1)
>>> clf2 = RandomForestClassifier(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]
>>> 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]
>>> 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)
>>>
"""
def __init__(self, estimators, voting='hard', weights=None, n_jobs=1,
flatten_transform=None):
self.estimators = estimators
self.voting = voting
self.weights = weights
self.n_jobs = n_jobs
self.flatten_transform = flatten_transform
@property
def named_estimators(self):
return dict(self.estimators)
[docs] def fit(self, X, y, sample_weight=None):
""" Fit the estimators.
Parameters
----------
X : {array-like, sparse matrix}, shape = [n_samples, n_features]
Training vectors, where n_samples is the number of samples and
n_features is the number of features.
y : array-like, shape = [n_samples]
Target values.
sample_weight : array-like, shape = [n_samples] or None
Sample weights. If None, then samples are equally weighted.
Note that this is supported only if all underlying estimators
support sample weights.
Returns
-------
self : object
"""
if isinstance(y, np.ndarray) and len(y.shape) > 1 and y.shape[1] > 1:
raise NotImplementedError('Multilabel and multi-output'
' classification is not supported.')
if self.voting not in ('soft', 'hard'):
raise ValueError("Voting must be 'soft' or 'hard'; got (voting=%r)"
% self.voting)
if self.estimators is None or len(self.estimators) == 0:
raise AttributeError('Invalid `estimators` attribute, `estimators`'
' should be a list of (string, estimator)'
' tuples')
if (self.weights is not None and
len(self.weights) != len(self.estimators)):
raise ValueError('Number of classifiers and weights must be equal'
'; got %d weights, %d estimators'
% (len(self.weights), len(self.estimators)))
if sample_weight is not None:
for name, step in self.estimators:
if not has_fit_parameter(step, 'sample_weight'):
raise ValueError('Underlying estimator \'%s\' does not'
' support sample weights.' % name)
names, clfs = zip(*self.estimators)
self._validate_names(names)
n_isnone = np.sum([clf is None for _, clf in self.estimators])
if n_isnone == len(self.estimators):
raise ValueError('All estimators are None. At least one is '
'required to be a classifier!')
self.le_ = LabelEncoder().fit(y)
self.classes_ = self.le_.classes_
self.estimators_ = []
transformed_y = self.le_.transform(y)
self.estimators_ = Parallel(n_jobs=self.n_jobs)(
delayed(_parallel_fit_estimator)(clone(clf), X, transformed_y,
sample_weight=sample_weight)
for clf in clfs if clf is not None)
return self
@property
def _weights_not_none(self):
"""Get the weights of not `None` estimators"""
if self.weights is None:
return None
return [w for est, w in zip(self.estimators,
self.weights) if est[1] is not None]
[docs] def predict(self, X):
""" Predict class labels for X.
Parameters
----------
X : {array-like, sparse matrix}, shape = [n_samples, n_features]
Training vectors, where n_samples is the number of samples and
n_features is the number of features.
Returns
----------
maj : array-like, shape = [n_samples]
Predicted class labels.
"""
check_is_fitted(self, 'estimators_')
if self.voting == 'soft':
maj = np.argmax(self.predict_proba(X), axis=1)
else: # 'hard' voting
predictions = self._predict(X)
maj = np.apply_along_axis(
lambda x: np.argmax(
np.bincount(x, weights=self._weights_not_none)),
axis=1, arr=predictions)
maj = self.le_.inverse_transform(maj)
return maj
def _collect_probas(self, X):
"""Collect results from clf.predict calls. """
return np.asarray([clf.predict_proba(X) for clf in self.estimators_])
def _predict_proba(self, X):
"""Predict class probabilities for X in 'soft' voting """
if self.voting == 'hard':
raise AttributeError("predict_proba is not available when"
" voting=%r" % self.voting)
check_is_fitted(self, 'estimators_')
avg = np.average(self._collect_probas(X), axis=0,
weights=self._weights_not_none)
return avg
@property
def predict_proba(self):
"""Compute probabilities of possible outcomes for samples in X.
Parameters
----------
X : {array-like, sparse matrix}, shape = [n_samples, n_features]
Training vectors, where n_samples is the number of samples and
n_features is the number of features.
Returns
----------
avg : array-like, shape = [n_samples, n_classes]
Weighted average probability for each class per sample.
"""
return self._predict_proba
def set_params(self, **params):
""" Setting the parameters for the voting classifier
Valid parameter keys can be listed with get_params().
Parameters
----------
params: keyword arguments
Specific parameters using e.g. set_params(parameter_name=new_value)
In addition, to setting the parameters of the ``VotingClassifier``,
the individual classifiers of the ``VotingClassifier`` can also be
set or replaced by setting them to None.
Examples
--------
# In this example, the RandomForestClassifier is removed
clf1 = LogisticRegression()
clf2 = RandomForestClassifier()
eclf = VotingClassifier(estimators=[('lr', clf1), ('rf', clf2)]
eclf.set_params(rf=None)
"""
super(VotingClassifier, self)._set_params('estimators', **params)
return self
def get_params(self, deep=True):
""" Get the parameters of the VotingClassifier
Parameters
----------
deep: bool
Setting it to True gets the various classifiers and the parameters
of the classifiers as well
"""
return super(VotingClassifier,
self)._get_params('estimators', deep=deep)
def _predict(self, X):
"""Collect results from clf.predict calls. """
return np.asarray([clf.predict(X) for clf in self.estimators_]).T
