迭代数组两次（笛卡尔积）但只考虑一半的元素 [英] Iterate over array twice (cartesian product) but consider only half the elements

问题描述

我试图迭代一个数组两次以获得元素对（e_i，e_j），但我只想要这样的元素，即i< j。

I am trying to iterate over an array twice to have pairs of elements (e_i,e_j) but I only want the elements such that i < j.

基本上，我想要的就像C语言一样。

Basically, what I want would look like this is C-like languages.

int my_array[N] = ...;
for (int i=0; i<N; i++)
        for (int j=i+1; j<N; j++)
                something(my_array[i],my_array[j]);

我在 itertools （我发现最接近的是 itertools.product（* iterables [，repeat]））。

I didn't find what I was looking for in itertools (the closest thing I've found was itertools.product(*iterables[, repeat])).

我尝试过一些事情，但我不相信任何事情：

I tried a few things but I am not really convinced by any of them :

my_list=range(10)

# Using enumerate and slices - explicit loop
res=[]
for i,j in enumerate(my_list):
        for k in my_list[i+1:]:
                res.append((j,k))
print res

# Using enumerate and slices - list comprehension
res=[(j,k) for i,j in enumerate(my_list) for k in my_list[i+1:]]
print res

# Using enumerate and xrange - explicit loop
res=[]
for i,j in enumerate(my_list):
        for k in range(i+1, len(my_list)):
                res.append((j,my_list[k]))
print res       

# Using enumerate and xrange - list comprehension
res=[(j,my_list[k]) for i,j in enumerate(my_list) for k in range(i+1, len(my_list))]
print res

我仍然相信有更好更多的pythonic解决方案。任何建议都是受欢迎的。

I'm still convinced that there is a better and more pythonic solution. Any suggestion is welcome.

推荐答案

只需使用 itertools.combinations（my_list，2）。

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