ValueError：不能将折叠数n_folds = 3大于样本数：2

Question

I can't figure out why am I getting this error, because I explicitly set cv=2, so how n_fold could be equal to 3? (I am using python 2 with anaconda)

import numpy as np
from sklearn.cross_validation import cross_val_score
from sklearn.linear_model import LogisticRegressionCV

classifier = LogisticRegressionCV(scoring='roc_auc')
x = np.array([[1, 2, 3], [3, 4, 9], [4, 9, 1], [8, 0, 4], [1, 1, 4], [1.1, 2, 4]])
y = np.array([True, False, True, False, True, False])
cross_val_score(classifier, x, y, cv=2)

After running the code I get: ValueError: Cannot have number of folds n_folds=3 greater than the number of samples: 2

Answer 1

Ah, my usage of LogisticRegressionCV was completely incorrect. Here is the valid one:

import numpy as np
from sklearn.linear_model import LogisticRegressionCV

classifier = LogisticRegressionCV(scoring='roc_auc', cv=2)
classifier.store_cv_values = True
x = np.array([[1, 2, 3], [3, 4, 9], [4, 9, 1], [8, 0, 4], [1, 1, 4], [1.1, 2, 4]])
y = np.array([True, False, True, False, True, False])
classifier.fit(x, y)