sklearn.multiclass
.OneVsRestClassifier¶

class
sklearn.multiclass.
OneVsRestClassifier
(estimator, *, n_jobs=None)[source]¶ Onevstherest (OvR) multiclass strategy.
Also known as onevsall, this strategy consists in fitting one classifier per class. For each classifier, the class is fitted against all the other classes. In addition to its computational efficiency (only
n_classes
classifiers are needed), one advantage of this approach is its interpretability. Since each class is represented by one and one classifier only, it is possible to gain knowledge about the class by inspecting its corresponding classifier. This is the most commonly used strategy for multiclass classification and is a fair default choice.OneVsRestClassifier can also be used for multilabel classification. To use this feature, provide an indicator matrix for the target
y
when calling.fit
. In other words, the target labels should be formatted as a 2D binary (0/1) matrix, where [i, j] == 1 indicates the presence of label j in sample i. This estimator uses the binary relevance method to perform multilabel classification, which involves training one binary classifier independently for each label.Read more in the User Guide.
 Parameters
 estimatorestimator object
An estimator object implementing fit and one of decision_function or predict_proba.
 n_jobsint, default=None
The number of jobs to use for the computation: the
n_classes
onevsrest problems are computed in parallel.None
means 1 unless in ajoblib.parallel_backend
context.1
means using all processors. See Glossary for more details.Changed in version v0.20:
n_jobs
default changed from 1 to None
 Attributes
 estimators_list of
n_classes
estimators Estimators used for predictions.
 coef_ndarray of shape (1, n_features) or (n_classes, n_features)
Coefficient of the features in the decision function. This attribute exists only if the
estimators_
definescoef_
. intercept_ndarray of shape (1, 1) or (n_classes, 1)
If
y
is binary, the shape is(1, 1)
else(n_classes, 1)
This attribute exists only if theestimators_
definesintercept_
. classes_array, shape = [
n_classes
] Class labels.
 n_classes_int
Number of classes.
 label_binarizer_LabelBinarizer object
Object used to transform multiclass labels to binary labels and viceversa.
multilabel_
booleanWhether this is a multilabel classifier
 estimators_list of
See also
sklearn.multioutput.MultiOutputClassifier
Alternate way of extending an estimator for multilabel classification.
sklearn.preprocessing.MultiLabelBinarizer
Transform iterable of iterables to binary indicator matrix.
Examples
>>> import numpy as np >>> from sklearn.multiclass import OneVsRestClassifier >>> from sklearn.svm import SVC >>> X = np.array([ ... [10, 10], ... [8, 10], ... [5, 5.5], ... [5.4, 5.5], ... [20, 20], ... [15, 20] ... ]) >>> y = np.array([0, 0, 1, 1, 2, 2]) >>> clf = OneVsRestClassifier(SVC()).fit(X, y) >>> clf.predict([[19, 20], [9, 9], [5, 5]]) array([2, 0, 1])
Methods
Returns the distance of each sample from the decision boundary for each class.
fit
(X, y)Fit underlying estimators.
get_params
([deep])Get parameters for this estimator.
partial_fit
(X, y[, classes])Partially fit underlying estimators
predict
(X)Predict multiclass targets using underlying estimators.
Probability estimates.
score
(X, y[, sample_weight])Return the mean accuracy on the given test data and labels.
set_params
(**params)Set the parameters of this estimator.

decision_function
(X)[source]¶ Returns the distance of each sample from the decision boundary for each class. This can only be used with estimators which implement the decision_function method.
 Parameters
 Xarraylike of shape (n_samples, n_features)
 Returns
 Tarraylike of shape (n_samples, n_classes)
Changed in version 0.19: output shape changed to
(n_samples,)
to conform to scikitlearn conventions for binary classification.

fit
(X, y)[source]¶ Fit underlying estimators.
 Parameters
 X(sparse) arraylike of shape (n_samples, n_features)
Data.
 y(sparse) arraylike of shape (n_samples,) or (n_samples, n_classes)
Multiclass targets. An indicator matrix turns on multilabel classification.
 Returns
 self

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
 paramsmapping of string to any
Parameter names mapped to their values.

property
multilabel_
¶ Whether this is a multilabel classifier

partial_fit
(X, y, classes=None)[source]¶ Partially fit underlying estimators
Should be used when memory is inefficient to train all data. Chunks of data can be passed in several iteration.
 Parameters
 X(sparse) arraylike of shape (n_samples, n_features)
Data.
 y(sparse) arraylike of shape (n_samples,) or (n_samples, n_classes)
Multiclass targets. An indicator matrix turns on multilabel classification.
 classesarray, shape (n_classes, )
Classes across all calls to partial_fit. Can be obtained via
np.unique(y_all)
, where y_all is the target vector of the entire dataset. This argument is only required in the first call of partial_fit and can be omitted in the subsequent calls.
 Returns
 self

predict
(X)[source]¶ Predict multiclass targets using underlying estimators.
 Parameters
 X(sparse) arraylike of shape (n_samples, n_features)
Data.
 Returns
 y(sparse) arraylike of shape (n_samples,) or (n_samples, n_classes)
Predicted multiclass targets.

predict_proba
(X)[source]¶ Probability estimates.
The returned estimates for all classes are ordered by label of classes.
Note that in the multilabel case, each sample can have any number of labels. This returns the marginal probability that the given sample has the label in question. For example, it is entirely consistent that two labels both have a 90% probability of applying to a given sample.
In the single label multiclass case, the rows of the returned matrix sum to 1.
 Parameters
 Xarraylike of shape (n_samples, n_features)
 Returns
 T(sparse) arraylike of shape (n_samples, n_classes)
Returns the probability of the sample for each class in the model, where classes are ordered as they are in
self.classes_
.

score
(X, y, sample_weight=None)[source]¶ Return the mean accuracy on the given test data and labels.
In multilabel 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
 Xarraylike of shape (n_samples, n_features)
Test samples.
 yarraylike of shape (n_samples,) or (n_samples, n_outputs)
True labels for X.
 sample_weightarraylike 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 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.