如何反转具有重复值的字典 [英] How to reverse a dictionary that has repeated values
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问题描述
我有一本字典,其中有将近100,000个(键,值)对,并且大多数键都映射到相同的值。例如:
I have a dictionary with almost 100,000 (key, value) pairs and the majority of the keys map to the same values. For example:
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,并映射到用于映射到 mydict
中该值的所有 mydict.keys()
的列表。因此,根据上面的示例,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 in mydict
. So based on the example above I would get:
reversed_dict = {1: ['a', 'b', 'h'], 2: ['c', 'e'] , 3: ['d', 'j']}
我来了提出了一个非常昂贵的解决方案,我想听听比这更有效的解决方案:
I came up with a solution that is very expensive and I want to hear any ideas for doing this more efficiently than this:
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)
推荐答案
from collections import defaultdict
reversed_dict = defaultdict(list)
for key, value in mydict.items():
reversed_dict[value].append(key)
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