如何获取列表中最不常见的元素? [英] How to get the least common element in a list?

问题描述

为了找到最常见的，我知道我可以使用这样的东西:

To find the most common, I know I can use something like this:

most_common = collections.Counter(list).most_common(to_find)

然而，我似乎无法找到任何可比的东西，以找到最不常见的元素.

However, I can't seem to find anything comparable, for finding the least common element.

我能得到关于如何做的建议吗.

Could I please get recommendations on how to do.

推荐答案

借用 collections.Counter.most_common 的来源并适当反转:

Borrowing the source of collections.Counter.most_common and inverting as appropriate:

from operator import itemgetter
import heapq
import collections
def least_common_values(array, to_find=None):
    counter = collections.Counter(array)
    if to_find is None:
        return sorted(counter.items(), key=itemgetter(1), reverse=False)
    return heapq.nsmallest(to_find, counter.items(), key=itemgetter(1))

>>> data = [1,1,2,2,2,2,3,3,3,3,3,3,3,4,4,4,4,4,4,4]
>>> least_common_values(data, 2)
[(1, 2), (2, 4)]
>>> least_common_values([1,1,2,3,3])
[(2, 1), (1, 2), (3, 2)]
>>>

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