如何仅使用itertools将Python列表的每个元素重复n次? [英] How to repeat each of a Python list's elements n times with itertools only?

问题描述

我有一个带有数字的列表: numbers = [1, 2, 3, 4].

I have a list with numbers: numbers = [1, 2, 3, 4].

我希望有一个列表，其中他们会重复n次(对于n = 3):

I would like to have a list where they repeat n times like so (for n = 3):

[1, 1, 1, 2, 2, 2, 3, 3, 3, 4, 4, 4].

问题是我只想使用itertools，因为我对性能的限制很大.

The problem is that I would like to only use itertools for this, since I am very constrained in performance.

我尝试使用此表达式:

list(itertools.chain.from_iterable(itertools.repeat(numbers, 3)))

但这给了我这种结果:

[1, 2, 3, 4, 1, 2, 3, 4, 1, 2, 3, 4]

这显然不是我所需要的.

which is obviously not what I need.

有没有办法仅使用itertools来执行此操作，而不使用排序，循环和列表推导?我能得到的最接近的是:

Is there a way to do this with itertools only, without using sorting, loops and list comprehensions? The closest I could get is:

list(itertools.chain.from_iterable([itertools.repeat(i, 3) for i in numbers]))，

但是它也使用列表理解，这是我想避免的.

but it also uses list comprehension, which I would like to avoid.

推荐答案

由于您不想使用列表推导，因此以下是一种纯粹的(+ zip)itertools方法-

Since you don't want to use list comprehension, following is a pure (+zip) itertools method to do it -

from itertools import chain, repeat

list(chain.from_iterable(zip(*repeat(numbers, 3))))
# [1, 1, 1, 2, 2, 2, 3, 3, 3, 4, 4, 4]

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