如何从k个项目列表中生成所有n个大小的集合？

Question

给定一组k项（例如，{1,2,3}，k=3），如何使用原始集的值生成所有可能的长度n集合？应该有k**n个此类列表。

Answer 1

您可以使用itertools模块：

>>> from itertools import permutations
>>> s = set((1,2,3))
>>> list(permutations(s))

[(1, 2, 3), (1, 3, 2), (2, 1, 3), (2, 3, 1), (3, 1, 2), (3, 2, 1)]

>>> list(permutations(s, 2))
[(1, 2), (1, 3), (2, 1), (2, 3), (3, 1), (3, 2)]

<强> 更新： 也许这更像是被要求的：

>>> from itertools import chain, combinations_with_replacement, permutations
>>> list(set(chain.from_iterable(permutations(x) for x in combinations_with_replacement(s, 3))))
[(1, 3, 2),
 (1, 3, 1),
 (3, 3, 1),
 (1, 1, 1),
 (3, 3, 3),
 (2, 3, 2),
 (3, 3, 2),
 (2, 3, 3),
 (2, 3, 1),
 (3, 2, 2),
 (3, 1, 3),
 (3, 2, 3),
 (3, 1, 2),
 (1, 2, 1),
 (3, 1, 1),
 (3, 2, 1),
 (1, 2, 2),
 (1, 2, 3),
 (2, 1, 2),
 (2, 2, 3),
 (2, 1, 3),
 (2, 2, 2),
 (1, 1, 3),
 (2, 1, 1),
 (1, 1, 2),
 (2, 2, 1),
 (1, 3, 3)]