python - 余弦相似度的简单实现有什么问题？

Question

在 blog post 中我读到以下余弦相似度的“天真实现”永远不应在生产中使用，博客文章没有解释原因，我真的很好奇，谁能给出解释？

import numpy as np

def cos_sim(a, b):
    """Takes 2 vectors a, b and returns the cosine similarity according 
    to the definition of the dot product
    """
    dot_product = np.dot(a, b)
    norm_a = np.linalg.norm(a)
    norm_b = np.linalg.norm(b)
    return dot_product / (norm_a * norm_b)

# the counts we computed above
sentence_m = np.array([1, 1, 1, 1, 0, 0, 0, 0, 0]) 
sentence_h = np.array([0, 0, 1, 1, 1, 1, 0, 0, 0])
sentence_w = np.array([0, 0, 0, 1, 0, 0, 1, 1, 1])

# We should expect sentence_m and sentence_h to be more similar
print(cos_sim(sentence_m, sentence_h)) # 0.5
print(cos_sim(sentence_m, sentence_w)) # 0.25

Answer 1

cos_sim 函数应该是这样的。问题是用 counts 表示句子。考虑 using tf-idf相反。