将dicts列表映射到dicts列表的dict中

Question

我甚至不确定该怎么称呼它,所以很难搜索.我有,例如,

people = [
    {"age": 22, "first": "John", "last": "Smith"},
    {"age": 22, "first": "Jane", "last": "Doe"},
    {"age": 41, "first": "Brian", "last": "Johnson"},
]

我想要类似的东西

people_by_age = {
    22: [
        {"first": "John", "last": "Smith"},
        {"first": "Jane", "last": "Doe"},

    ],
    41: [
        {"first": "Brian", "last": "Johnson"}
    ]
}

在Python 2中最干净的方法是什么？

Answer 1

只需循环并添加到新词典:

people_by_age = {}
for person in people:
    age = person.pop('age')
    people_by_age.setdefault(age, []).append(person)

该dict.setdefault()方法返回给定键的现有值,或者如果缺少键,则使用第二个参数首先设置该键.

演示:

>>> people = [
...     {"age": 22, "first": "John", "last": "Smith"},
...     {"age": 22, "first": "Jane", "last": "Doe"},
...     {"age": 41, "first": "Brian", "last": "Johnson"},
... ]
>>> people_by_age = {}
>>> for person in people:
...     age = person.pop('age')
...     people_by_age.setdefault(age, []).append(person)
... 
>>> people_by_age
{41: [{'last': 'Johnson', 'first': 'Brian'}], 22: [{'last': 'Smith', 'first': 'John'}, {'last': 'Doe', 'first': 'Jane'}]}
>>> from pprint import pprint
>>> pprint(people_by_age)
{22: [{'first': 'John', 'last': 'Smith'}, {'first': 'Jane', 'last': 'Doe'}],
 41: [{'first': 'Brian', 'last': 'Johnson'}]}