带有 .index() 方法的 Python OrderedSet

2022-01-17 00:00:00 python set html-lists

问题描述

有谁知道 python 的快速 OrderedSet 实现:

Does anyone know about a fast OrderedSet implementation for python that:

  • 记住广告顺序
  • 有一个 index() 方法(就像列表提供的那样)

我发现的所有实现都缺少 .index() 方法.

All implementations I found are missing the .index() method.

解决方案

您可以随时将其添加到子类中.这是您在评论中链接的 OrderedSet 的基本实现:

You can always add it in a subclass. Here is a basic implementation for the OrderedSet you linked in a comment:

class IndexOrderedSet(OrderedSet):
    def index(self, elem):
        if key in self.map:
            return next(i for i, e in enumerate(self) if e == elem)
        else:
            raise KeyError("That element isn't in the set")

您提到您只需要 add、index 和按顺序迭代.您可以通过使用 OrderedDict 作为存储来获得它.作为奖励，您可以继承 collections.Set 抽象类以获得其他集合操作 frozenset 的支持:

You mentioned you only need add, index, and in-order iteration. You can get this by using an OrderedDict as storage. As a bonus, you can subclass the collections.Set abstract class to get the other set operations frozensets support:

from itertools import count, izip
from collections import OrderedDict, Set

class IndexOrderedSet(Set):
    """An OrderedFrozenSet-like object
       Allows constant time 'index'ing
       But doesn't allow you to remove elements"""
    def __init__(self, iterable = ()):
        self.num = count()
        self.dict = OrderedDict(izip(iterable, self.num))
    def add(self, elem):
        if elem not in self:
            self.dict[elem] = next(self.num)
    def index(self, elem):
        return self.dict[elem]
    def __contains__(self, elem):
        return elem in self.dict
    def __len__(self):
        return len(self.dict)
    def __iter__(self):
        return iter(self.dict)
    def __repr__(self):
        return 'IndexOrderedSet({})'.format(self.dict.keys())

你不能继承 collections.MutableSet 因为你不能支持从集合中移除元素并保持索引正确.

You can't subclass collections.MutableSet because you can't support removing elements from the set and keep the indexes correct.

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