sklearn.multiclass
.OneVsOneClassifier¶

class
sklearn.multiclass.
OneVsOneClassifier
(estimator, *, n_jobs=None)[source]¶ Onevsone multiclass strategy
This strategy consists in fitting one classifier per class pair. At prediction time, the class which received the most votes is selected. Since it requires to fit
n_classes * (n_classes  1) / 2
classifiers, this method is usually slower than onevstherest, due to its O(n_classes^2) complexity. However, this method may be advantageous for algorithms such as kernel algorithms which don’t scale well withn_samples
. This is because each individual learning problem only involves a small subset of the data whereas, with onevstherest, the complete dataset is usedn_classes
times.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 * ( n_classes  1) / 2
OVO problems are computed in parallel.None
means 1 unless in ajoblib.parallel_backend
context.1
means using all processors. See Glossary for more details.
 Attributes
 estimators_list of
n_classes * (n_classes  1) / 2
estimators Estimators used for predictions.
 classes_numpy array of shape [n_classes]
Array containing labels.
 n_classes_int
Number of classes
 pairwise_indices_list, length =
len(estimators_)
, orNone
Indices of samples used when training the estimators.
None
whenestimator
’spairwise
tag is False.Deprecated since version 0.24: The _pairwise attribute is deprecated in 0.24. From 1.1 (renaming of 0.25) and onward,
pairwise_indices_
will use the pairwise estimator tag instead.
 estimators_list of
Examples
>>> from sklearn.datasets import load_iris >>> from sklearn.model_selection import train_test_split >>> from sklearn.multiclass import OneVsOneClassifier >>> from sklearn.svm import LinearSVC >>> X, y = load_iris(return_X_y=True) >>> X_train, X_test, y_train, y_test = train_test_split( ... X, y, test_size=0.33, shuffle=True, random_state=0) >>> clf = OneVsOneClassifier( ... LinearSVC(random_state=0)).fit(X_train, y_train) >>> clf.predict(X_test[:10]) array([2, 1, 0, 2, 0, 2, 0, 1, 1, 1])
Methods
Decision function for the OneVsOneClassifier.
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)Estimate the best class label for each sample 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 this estimator.

decision_function
(X)[source]¶ Decision function for the OneVsOneClassifier.
The decision values for the samples are computed by adding the normalized sum of pairwise classification confidence levels to the votes in order to disambiguate between the decision values when the votes for all the classes are equal leading to a tie.
 Parameters
 Xarraylike of shape (n_samples, n_features)
 Returns
 Yarraylike of shape (n_samples, n_classes) or (n_samples,) for binary classification.
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.
 yarraylike of shape (n_samples,)
Multiclass targets.
 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
 paramsdict
Parameter names mapped to their values.

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, where the first call should have an array of all target variables.
 Parameters
 X(sparse) arraylike of shape (n_samples, n_features)
Data.
 yarraylike of shape (n_samples,)
Multiclass targets.
 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]¶ Estimate the best class label for each sample in X.
This is implemented as
argmax(decision_function(X), axis=1)
which will return the label of the class with most votes by estimators predicting the outcome of a decision for each possible class pair. Parameters
 X(sparse) arraylike of shape (n_samples, n_features)
Data.
 Returns
 ynumpy array of shape [n_samples]
Predicted multiclass targets.

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
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.