def test_calibration_prefit():
"""Test calibration for prefitted classifiers"""
n_samples = 50
X, y = make_classification(n_samples=3 * n_samples, n_features=6,
random_state=42)
sample_weight = np.random.RandomState(seed=42).uniform(size=y.size)
X -= X.min() # MultinomialNB only allows positive X
# split train and test
X_train, y_train, sw_train = \
X[:n_samples], y[:n_samples], sample_weight[:n_samples]
X_calib, y_calib, sw_calib = \
X[n_samples:2 * n_samples], y[n_samples:2 * n_samples], \
sample_weight[n_samples:2 * n_samples]
X_test, y_test = X[2 * n_samples:], y[2 * n_samples:]
# Naive-Bayes
clf = MultinomialNB()
clf.fit(X_train, y_train, sw_train)
prob_pos_clf = clf.predict_proba(X_test)[:, 1]
# Naive Bayes with calibration
for this_X_calib, this_X_test in [(X_calib, X_test),
(sparse.csr_matrix(X_calib),
sparse.csr_matrix(X_test))]:
for method in ['isotonic', 'sigmoid']:
pc_clf = CalibratedClassifierCV(clf, method=method, cv="prefit")
for sw in [sw_calib, None]:
pc_clf.fit(this_X_calib, y_calib, sample_weight=sw)
y_prob = pc_clf.predict_proba(this_X_test)
y_pred = pc_clf.predict(this_X_test)
prob_pos_pc_clf = y_prob[:, 1]
assert_array_equal(y_pred,
np.array([0, 1])[np.argmax(y_prob, axis=1)])
assert_greater(brier_score_loss(y_test, prob_pos_clf),
brier_score_loss(y_test, prob_pos_pc_clf))
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