如何仅使用 itertools 将 Python 列表的每个元素重复 n 次?
问题描述
我有一个带有数字的列表:数字 = [1, 2, 3, 4].
I have a list with numbers:
numbers = [1, 2, 3, 4].
我想要一个列表，他们像这样重复 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].
问题是我只想为此使用 itertools，因为我的性能非常有限.
The problem is that I would like to only use itertools for this, since I am very constrained in performance.
我尝试使用这个表达式:
I tried to use this expression:
list(itertools.chain.from_iterable(itertools.repeat(numbers, 3)))
但它给了我这样的结果:
But it gives me this kind of result:
[1, 2, 3, 4, 1, 2, 3, 4, 1, 2, 3, 4]
这显然不是我需要的.
有没有办法只使用 itertools 来做到这一点，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])),
但它也使用列表理解，我想避免.
but it also uses list comprehension, which I would like to avoid.
解决方案
由于不想使用列表推导式，下面是纯(+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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