Python 按值分组字典，返回键和值列表对

考虑一个具有多个重复值的字典。如何按值对词典进行分组？例如：

mydict = 
{
    'germany': 'europe', 
    'france': 'europe',
    'canada': 'north america', 
    'latvia': 'europe'
    'usa': 'north america',
    'china': 'asia'
}

按值分组到列表中

groupdDict =
{
    'europe': ['germany','france','latvia'],
    'north america': ['canada','usa'],
    'asia': ['china']
}

---

使用

collections.defaultdict

演示：

mydict ={
        'germany': 'europe',
        'france': 'europe',
        'canada': 'north america',
        'latvia': 'europe',
        'usa': 'north america',
        'china': 'asia'
    }

import collections
d = collections.defaultdict(list)
for k,v in mydict.items():
    d[v].append(k)
print(d)

d = {}
for k,v in mydict.items():
    if v not in d:
        d[v] = []
    d[v].append(k)
print(d)

{'north america': ['canada', 'usa'], 'europe': ['france', 'latvia', 'germany'], 'asia': ['china']}

或者使用简单的迭代

演示：

mydict ={
        'germany': 'europe',
        'france': 'europe',
        'canada': 'north america',
        'latvia': 'europe',
        'usa': 'north america',
        'china': 'asia'
    }

import collections
d = collections.defaultdict(list)
for k,v in mydict.items():
    d[v].append(k)
print(d)

d = {}
for k,v in mydict.items():
    if v not in d:
        d[v] = []
    d[v].append(k)
print(d)

{'north america': ['canada', 'usa'], 'europe': ['france', 'latvia', 'germany'], 'asia': ['china']}

输出：

mydict ={
        'germany': 'europe',
        'france': 'europe',
        'canada': 'north america',
        'latvia': 'europe',
        'usa': 'north america',
        'china': 'asia'
    }

import collections
d = collections.defaultdict(list)
for k,v in mydict.items():
    d[v].append(k)
print(d)

d = {}
for k,v in mydict.items():
    if v not in d:
        d[v] = []
    d[v].append(k)
print(d)

{'north america': ['canada', 'usa'], 'europe': ['france', 'latvia', 'germany'], 'asia': ['china']}