使用itertools重复编号

Question

我正在学习itertools，并遇到了一个有趣的问题。

如何获得以下结果？

nums = [1,2,3,4]
# logic:  i+1 th number is repeated i times.
          2 is repeated 1 times and 4 is repeated 3 times.

required = [2,4,4,4] 

我的尝试

import itertools

nums = [1,2,3,4]
nums[::2]  # [1,3]
nums[1::2] # [2,4]
              * 2 is repeated 1 times
                * 4 is repeated 3 times and makes [2,4,4,4]

list(itertools.starmap(itertools.repeat, zip(nums[::2],nums[1::2])))

Gives,
[repeat(1, 2), repeat(3, 4)]

How to get:
required = [2,4,4,4]

必填

From: [1,2,3,4]
To:   [2,4,4,4]

We can use itertools, list comp and numpy.

Answer 1

您不需要itertools。列表理解和邮政编码就足够了：

nums = [1,2,3,4]

rnums = [ rn for r,n in zip(nums[::2],nums[1::2]) for rn in r*[n] ]

print(rnums) # [2, 4, 4, 4]