余弦相似度

问题描述

我计算了两个文件的tf / idf值。以下是tf / idf值：

I calculated tf/idf values of two documents. The following are the tf/idf values:

1.txt
0.0
0.5
2.txt
0.0
0.5

文件如下：

1.txt = > dog cat
2.txt = > cat elephant

如何使用这些值来计算余弦相似度？

我知道我应该计算点积，然后通过它找到距离并除以点积。如何使用我的值来计算？

I know that I should calculate the dot product, then find distance and divide dot product by it. How can I calculate this using my values?

还有一个问题：这两个文档的单词数量是否相同是否重要？

推荐答案

            a * b
sim(a,b) =--------
           |a|*|b|

a * b是点积

一些细节：

def dot(a,b):
  n = length(a)
  sum = 0
  for i in xrange(n):
    sum += a[i] * b[i];
  return sum

def norm(a):
  n = length(a)
  for i in xrange(n):
    sum += a[i] * a[i]
  return math.sqrt(sum)

def cossim(a,b):
  return dot(a,b) / (norm(a) * norm(b))

是。在某种程度上，a和b必须具有相同的长度。但是a和b通常都有稀疏表示，你只需要存储非零项，你就可以更快地计算norm和dot。

yes. to some extent, a and b must have the same length. but a and b usually have sparse representation, you only need to store non-zero entries and you can calculate norm and dot more fast.

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