CODEWITHSUNDEEP
svmscikit-learn
lizarisk
lizarisk

Reputation: 7820

How to use OneVsRestClassifier with SVC for multilabel problems?

I'm using OneVsRestClassifier for multilabel classification. It works with LinearSVC, but when I apply it to SVC, the following error appears:

classifier = OneVsRestClassifier(SVC(class_weight='balanced'))
classifier.fit(X1, y1)
y2 = classifier.predict(X2)

Traceback (most recent call last):
...
File "/usr/local/lib/python2.7/dist-packages/sklearn/multiclass.py", line 219, in predict
  return predict_ovr(self.estimators_, self.label_binarizer_, X)
File "/usr/local/lib/python2.7/dist-packages/sklearn/multiclass.py", line 93, in predict_ovr
  Y = np.array([_predict_binary(e, X) for e in estimators])
File "/usr/local/lib/python2.7/dist-packages/sklearn/multiclass.py", line 66, in _predict_binary
  score = estimator.predict_proba(X)[:, 1]
File "/usr/local/lib/python2.7/dist-packages/sklearn/svm/base.py", line 490, in predict_proba
  "probability estimates must be enabled to use this method")
NotImplementedError: probability estimates must be enabled to use this method</code>

Does anybody know what is it?

Upvotes: 3

Views: 3661

Answers (1)

Fred Foo
Fred Foo

Reputation: 363547

This is a bug. The OneVsRestClassifier calls the predict_proba method when it finds one, but the one on SVC does not actually work unless you construct it with probability=True to get Platt scaling (which I don't actually encourage).

The reason that it works for LinearSVC is that that class does not have a predict_proba, so OvR backs off to the decision_function method.

Upvotes: 5

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