在 Python (Powerset) 中获取一个集合的所有子集

作者

在 Python 中获取一个集合的所有子集（幂集）

Get all subsets of a Set in Python (Powerset)

使用itertools文档中的方法获取 a 的所有子集
set。

主程序
from itertools import chain, combinations


def powerset(iterable):
    "powerset([1,2,3]) --> () (1,) (2,) (3,) (1,2) (1,3) (2,3) (1,2,3)"
    s = list(iterable)
    return chain.from_iterable(combinations(s, r) for r in range(len(s)+1))


# print(list(combinations([1, 2, 3], 2)))

my_set = {1, 2, 3}

# 👇️ [(), (1,), (2,), (3,), (1, 2), (1, 3), (2, 3), (1, 2, 3)]
print(list(powerset(my_set)))

该powerset配方在
文档的这一部分中可用。

itertools.combinations()方法采用

可迭代和长度参数。

该方法从 iterable 返回长度为 N 的元素的子序列。

主程序
from itertools import combinations


# 👇️ [()]
print(list(combinations([1, 2, 3], 0)))

# 👇️ [(1,), (2,), (3,)]
print(list(combinations([1, 2, 3], 1)))

# 👇️ [(1, 2), (1, 3), (2, 3)]
print(list(combinations([1, 2, 3], 2)))

# 👇️ [(1, 2, 3)]
print(list(combinations([1, 2, 3], 3)))

最后一步是使用
chain.from_iterable
方法。

该方法从可迭代对象中获取链式输入，例如['ABC', 'DEF']变成
A B C D E F.

主程序
from itertools import chain


# 👇️ [(), (1,), (2,), (3,), (1, 2), (1, 3), (2, 3)]
print(list(chain.from_iterable([
    [()],
    [(1,), (2,), (3,)],
    [(1, 2), (1, 3), (2, 3)],
])))

The chain.from_iterable() method returns a chain object. Use the list()
class to convert it to a list of tuples if necessary.

Alternatively, you can define your own function.

main.py
def powerset(iterable):
    l = list(iterable)

    result = [tuple()]

    for item in l:
        result += [tup + (item,) for tup in result]

    return result


my_set = {1, 2, 3}

# [(), (1,), (2,), (1, 2), (3,), (1, 3), (2, 3), (1, 2, 3)]
print(powerset(my_set))

The function converts the set to a list and uses a for loop to iterate over
the list.

On each iteration, we use a list comprehension to iterate over the result
variable. The result variable stores a list of tuples.

We used the addition (+) operator to combine two lists of tuples.

main.py
print([()] + [(1, 2)])  # 👉️ [(), (1, 2)]

print((1, 2) + (3, 4))  # 👉️ (1, 2, 3, 4)

We also used the operator to combine the elements of two tuples into a single
tuple.

Which approach you pick is a matter of personal preference. I’d use the recipe
from the documentation as it is quite performant, tried and tested.

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