'Count and smooth feature occurrences.'

def _count(self, X, Y):

    if np.any(((X.data if issparse(X) else X) < 0)):
        raise ValueError('Input    X    must    be    non-negative')
    self.feature_count_ += safe_sparse_dot(Y.T, X)
    self.class_count_ += Y.sum(axis=0)
