Returns an indicator vector where ith element = 1 if x_i is labeled by
    at least two LFs that give it disagreeing labels.

def _conflicted_data_points(L):
    """Returns an indicator vector where ith element = 1 if x_i is labeled by
    at least two LFs that give it disagreeing labels."""
    m = sparse.diags(np.ravel(L.max(axis=1).todense()))
    return np.ravel(np.max(m @ (L != 0) != L, axis=1).astype(int).todense())