I'm having trouble figuring out how to use the cross validation scoring
function. As far as I can tell, I'm exactly following the tutorial given
here:
http://scikit-learn.org/0.13/modules/cross_validation.html#computing-cross-validated-metrics
Paraphrase of code:
from sklearn import naive_bayes
from sklearn import cross_validation
from sklearn import metrics
alg = naive_bayes.GaussianNB()
folds = 10
//...data loaded here into x and y
score = cross_validation.cross_val_score(alg, x, y, cv=folds,
scoring=metrics.accuracy_score)
The error I get is:
Error:
Traceback (most recent call last):
File "pylearn.py", line 431, in <module>
l = Learn()
File "pylearn.py", line 173, in __init__
scores = self.crossVal(x, y, alg, args.cross_val[0])
File "pylearn.py", line 241, in crossVal
score = cross_validation.cross_val_score(alg, x, y, cv=folds,
scoring=metrics.f1_score)
File
"/usr/local/lib64/python2.7/site-packages/sklearn/cross_validation.py",
line 1174, in cross_val_score
for train, test in cv)
File
"/usr/local/lib64/python2.7/site-packages/sklearn/externals/joblib/parallel.py",
line 514, in __call__
self.dispatch(function, args, kwargs)
File
"/usr/local/lib64/python2.7/site-packages/sklearn/externals/joblib/parallel.py",
line 311, in dispatch
job = ImmediateApply(func, args, kwargs)
File
"/usr/local/lib64/python2.7/site-packages/sklearn/externals/joblib/parallel.py",
line 135, in __init__
self.results = func(*args, **kwargs)
File
"/usr/local/lib64/python2.7/site-packages/sklearn/cross_validation.py",
line 1081, in _cross_val_score
score = scorer(estimator, X_test, y_test)
File
"/usr/local/lib64/python2.7/site-packages/sklearn/metrics/metrics.py", line
1212, in f1_score
pos_label=pos_label, average=average)
File
"/usr/local/lib64/python2.7/site-packages/sklearn/metrics/metrics.py", line
1359, in fbeta_score
average=average)
File
"/usr/local/lib64/python2.7/site-packages/sklearn/metrics/metrics.py", line
1635, in precision_recall_fscore_support
y_type, y_true, y_pred = _check_clf_targets(y_true, y_pred)
File
"/usr/local/lib64/python2.7/site-packages/sklearn/metrics/metrics.py", line
162, in _check_clf_targets
y_true, y_pred = check_arrays(y_true, y_pred, allow_lists=True)
File
"/usr/local/lib64/python2.7/site-packages/sklearn/utils/validation.py",
line 181, in check_arrays
n_samples = _num_samples(arrays[0])
File
"/usr/local/lib64/python2.7/site-packages/sklearn/utils/validation.py",
line 123, in _num_samples
raise TypeError("Expected sequence or array-like, got %r" % x)
TypeError: Expected sequence or array-like, got GaussianNB()
Could anyone tell me what I'm doing wrong? Does cross_val_score only work
with certain classifiers?
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