fix test failure

    features = []

    similarity_xs = similarity * np.sign(w)

    for similarity_x in similarity_xs:

      pair = zip(similarity_x, range(len(similarity_x)))

      pair = list(zip(similarity_x, range(len(similarity_x))))

      pair.sort(key=lambda x: x[0], reverse=True)

      if pair[0][0] >= 1:

        pair = pair[1:self.K + 1]