使在Python的组合 [英] Making combinations in python

问题描述

我有四个值

age = 23
gender = "M"
city ="Delhi"
religion = "Muslim"

我需要这些安排的每一种组合与空值，例如 -

I need these arranged by every combination with empty values like -

23 * * *
23 M * *
23 M Delhi *
23 M Delhi Muslim
* M * *
* M Delhi *
* M Delhi Muslim
* * Delhi *
* * Delhi Muslim
* * * Muslim
* * * *

我需要这个安排的维数在列表中按升序排列。因此，组合用一个数值应该在最前面。我有一些30+的属性，所以我需要一个自动化的方式来做到这一点在Python

I need this arranged by the number of dimensions in ascending order in a list. So combinations with one value should be on top. I have some 30+ attributes, so i need an automated way to do this in Python

任何想法？

推荐答案

NPE的回答通过构建完整的解决问题在存储器子集的列表，然后分拣它。这需要O（2 ^{的 N 的}）的空间和O（ N 的 ² 2 ^{的 N} ）的时间。如果这是不可接受的，那么这里有一个方法来生成在澳亚群（ N 的）空间和O（ N 的2 ^{的 N 的}）的时间。

NPE's answer solves the problem by constructing the full list of subsets in memory and then sorting it. This requires O(2ⁿ) space and O(n² 2ⁿ) time. If this is unacceptable, then here's a way to generate the subsets in O(n) space and O(n 2ⁿ) time.

from itertools import combinations

def subsets(s, placeholder = None):
    """
    Generate the subsets of `s` in order of size.
    Use `placeholder` for missing elements (default: None).
    """
    s = list(s)
    n = len(s)
    r = range(n)
    for i in range(n + 1):
        for c in combinations(r, i):
            result = [placeholder] * n
            for j in c:
                result[j] = s[j]
            yield result

>>> from pprint import pprint
>>> pprint(list(subsets([23, 'M', 'Delhi', 'Muslim'])))
[[None, None, None, None],
 [23, None, None, None],
 [None, 'M', None, None],
 [None, None, 'Delhi', None],
 [None, None, None, 'Muslim'],
 [23, 'M', None, None],
 [23, None, 'Delhi', None],
 [23, None, None, 'Muslim'],
 [None, 'M', 'Delhi', None],
 [None, 'M', None, 'Muslim'],
 [None, None, 'Delhi', 'Muslim'],
 [23, 'M', 'Delhi', None],
 [23, 'M', None, 'Muslim'],
 [23, None, 'Delhi', 'Muslim'],
 [None, 'M', 'Delhi', 'Muslim'],
 [23, 'M', 'Delhi', 'Muslim']]

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