如何反转具有重复值的字典 [英] How to reverse a dictionary that it has repeated values

问题描述

因此，我有一本字典，其中包含将近100,000个(键，值)对，并且大多数键都映射到相同的值.例如，想象一下这样的事情:

So, I have a dictionary with almost 100,000 (key, values) pairs and the majority of the keys map to the same values. For example imagine something like that:

mydict =  {'a': 1, 'c': 2, 'b': 1, 'e': 2, 'd': 3, 'h': 1, 'j': 3}

我想做的是反转字典，以便mydict中的每个值都将成为reverse_dict的键，并要映射到用于映射到该值的所有mydict.keys的列表.在神秘的故事.因此，根据以上示例，我将得到:

What I want to do, is to reverse the dictionary so that each value in mydict is going to be a key at the reverse_dict and is going to map to a list of all the mydict.keys that used to map to that value at the mydict. So based on the example above I would get:

reversed_dict = {1: ['a', 'b', 'h'], 2:['e', 'c'] , 3:['d', 'j']} 

我想出了一个非常昂贵的解决方案，我真的想听听任何比我更有效的想法.

I came up with a solution that is very expensive and I would really want to hear any ideas more efficient than mine.

我昂贵的解决方案:

reversed_dict = {}
for value in mydict.values():
    reversed_dict[value] = []
    for key in mydict.keys():
        if mydict[key] == value:
            if key not in reversed_dict[value]: reversed_dict[value].append(key)

Output >> reversed_dict = {1: ['a', 'b', 'h'], 2: ['c', 'e'], 3: ['d', 'j']}

我真的很高兴听到比我的想法更好，更有效的想法. 谢谢！

I would really appreciate to hear any ideas better and more efficient than than mine. Thanks!

推荐答案

from collections import defaultdict

reversed_dict = defaultdict(list)
for key, value in mydict.items():
    reversed_dict[value].append(key)

请不要将dict用作变量，这会与内置函数dict()冲突

Please do not use dict as a variable, this collides with builtin function dict()

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