如何在Python中通过单个字典的键对一堆列表进行分组

Question

我有一堆列表，其中包含彼此相关的元素，我想将它们转换为单个字典，其中列表作为值：

list1 = ['cat', 'animal']
list2 = ['dog', 'animal']
list3 = ['crow', 'bird']

result = {'animal': ['cat', 'dog'], 'bird': 'crow'}

我怎么能这么做呢？

Answer 1

简单的方法：

data = [['cat', 'animal'], ['dog', 'animal'], ['crow', 'bird']]

result = {}

for value, key in data:
    result[key] = result.get(key, []) + [value]

result #=> {'bird': ['crow'], 'animal': ['cat', 'dog']}

使用defaultdict：

from collections import defaultdict

data = [['cat', 'animal'], ['dog', 'animal'], ['crow', 'bird']]

result = defaultdict(list)

for value, key in data:
    result[key].append(value)

result #=> defaultdict(<class 'list'>, {'animal': ['cat', 'dog'], 'bird': ['crow']})

使用groupby来自itertools：

from itertools import groupby

data = [['cat', 'animal'], ['dog', 'animal'], ['crow', 'bird']]

{k: [x[0] for x in g] for k, g in groupby(data, lambda x: x[1])}
#=> {'bird': ['crow'], 'animal': ['cat', 'dog']}

使用reduce来自functools：

from functools import reduce

data = [['cat', 'animal'], ['dog', 'animal'], ['crow', 'bird']]

reduce(lambda a, e: dict(a, **{e[1]: a.get(e[1], []) + [e[0]]}), data, {})
#=> {'bird': ['crow'], 'animal': ['cat', 'dog']}