Python:带有生成器的给定集合的幂集
问题描述
我正在尝试使用 generators 在 Python 中构建给定集合的子集列表.说我有
I am trying to build a list of subsets of a given set in Python with generators. Say I have
set([1, 2, 3])
作为输入，我应该有
[set([1, 2, 3]), set([2, 3]), set([1, 3]), set([3]), set([1, 2]), set([2]), set([1]), set([])]
作为输出.我怎样才能做到这一点?
as output. How can I achieve this?
解决方案
最快的方法是使用itertools，尤其是chain和combinations:
The fastest way is by using itertools, especially chain and combinations:
>>> from itertools import chain, combinations
>>> i = set([1, 2, 3])
>>> for z in chain.from_iterable(combinations(i, r) for r in range(len(i)+1)):
print z
()
(1,)
(2,)
(3,)
(1, 2)
(1, 3)
(2, 3)
(1, 2, 3)
>>>
如果您需要生成器，只需使用 yield 并将元组转换为集合:
If you need a generator just use yield and turn tuples into sets:
def powerset_generator(i):
for subset in chain.from_iterable(combinations(i, r) for r in range(len(i)+1)):
yield set(subset)
然后简单地说:
>>> for i in powerset_generator(i):
print i
set([])
set([1])
set([2])
set([3])
set([1, 2])
set([1, 3])
set([2, 3])
set([1, 2, 3])
>>>
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