python 相当于 filter() 获取两个输出列表(即列表的分区) [英] python equivalent of filter() getting two output lists (i.e. partition of a list)

问题描述

假设我有一个列表和一个过滤功能.使用类似

<预><代码>>>>过滤器(λ x:x > 10，[1,4,12,7,42])[12, 42]

我可以获得符合条件的元素.有没有我可以使用的函数来输出两个列表，一个匹配的元素，一个剩余的元素?我可以调用 filter() 函数两次，但这有点难看 :)

元素的顺序应该是守恒的，我可能有多次相同的元素.

解决方案

试试这个:

def partition(pred, iterable):真= []假= []对于可迭代项目:如果预测(项目):trues.append(item)别的:falses.append(item)返回真，假

用法:

<预><代码>>>>trues, falses = partition(lambda x: x > 10, [1,4,12,7,42])>>>真的[12, 42]>>>假的[1, 4, 7]

itertools recipes 中还有一个实现建议:

from itertools import filterfalse, tee定义分区(pred，可迭代):'使用谓词将条目划分为虚假条目和真实条目'# partition(is_odd, range(10)) -->0 2 4 6 8 和 1 3 5 7 9t1, t2 = tee(可迭代)返回 filterfalse(pred, t1), filter(pred, t2)

配方来自 Python 3.x 文档.在 Python 2.x 中，filterfalse 被称为 ifilterfalse.

Let's say I have a list, and a filtering function. Using something like

>>> filter(lambda x: x > 10, [1,4,12,7,42])
[12, 42]

I can get the elements matching the criterion. Is there a function I could use that would output two lists, one of elements matching, one of the remaining elements? I could call the filter() function twice, but that's kinda ugly :)

Edit: the order of elements should be conserved, and I may have identical elements multiple times.

解决方案

Try this:

def partition(pred, iterable):
    trues = []
    falses = []
    for item in iterable:
        if pred(item):
            trues.append(item)
        else:
            falses.append(item)
    return trues, falses

Usage:

>>> trues, falses = partition(lambda x: x > 10, [1,4,12,7,42])
>>> trues
[12, 42]
>>> falses
[1, 4, 7]

There is also an implementation suggestion in itertools recipes:

from itertools import filterfalse, tee

def partition(pred, iterable):
    'Use a predicate to partition entries into false entries and true entries'
    # partition(is_odd, range(10)) --> 0 2 4 6 8   and  1 3 5 7 9
    t1, t2 = tee(iterable)
    return filterfalse(pred, t1), filter(pred, t2)

The recipe comes from the Python 3.x documentation. In Python 2.x filterfalse is called ifilterfalse.

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