def delete(self, doc):
        if doc.id is None:
            raise DatabaseException('Document does not have id')
        if doc.sid is None:
            try:
                rs = self.db.docs.remove({'id': doc.id}, safe=True)
                assert rs['n'] == 1
            except Exception as e:
                raise DatabaseException(e)
            return None
        doc.data = None
        return self.update(doc)
def permutation_subjects(y):
    """Permute class labels of Contextual Disorder dataset.
    """
    y_perm = np.random.randint(0, 2, len(y)/2)
    y_perm = np.concatenate((y_perm, np.logical_not(y_perm).astype(int)))
    return y_perm