反向查找字典

Question

我有下面的字典，我想做一个反向查找

countries_dict = {'Andorra': ('Europe', 'Andorra la Vella'),
              'Afghanistan': ('Asia', 'Kabul'),
              'Antigua and Barbuda': ('North America', "St. John's"),
              'Albania': ('Europe', 'Tirana'),
              'Armenia': ('Asia', 'Yerevan'),
              'Angola': ('Africa', 'Luanda'),
              'Argentina': ('South America', 'Buenos Aires'),
              'Austria': ('Europe', 'Vienna'),
              'Australia': ('Oceania', 'Canberra'),
              'Azerbaijan': ('Asia', 'Baku'),
              'Barbados': ('North America', 'Bridgetown'),
              'Bangladesh': ('Asia', 'Dhaka'),
              'Belgium': ('Europe', 'Brussels')}

我的代码如下所示：

def create_continents_dict(dct = dict) -> dict:
    reversed_dictionary = {value[0] : key for (key, value) in dct.items()}
    return reversed_dictionary

print(create_continents_dict(countries_dict))

{'Europe': 'Belgium', 'Asia': 'Bangladesh', 'North America': 'Barbados', 'Africa': 'Angola', 'South America': 'Argentina', 'Oceania': 'Australia'}

然而，我只得到最后一个它作为值查找的国家。我想要的是作为国家列表的值。有了上面的代码，我希望每个拥有同一个大陆的国家，都应该在列表中，对吗

{'Europe': ['Andorra', 'Albania', 'Austria', 'Belgium'] 'Asia': ['Afghanistan', 'Armenia', 'Azerbaijan', 'Bangladesh'], 'North America': ['Antigua and Barbuda', 'Barbados'], 'Africa': ['Angola'], 'South America': ['Argentina'], 'Oceania': ['Australia']}

Answer 1

试一试

from collections import defaultdict 
countries_dict = {'Andorra': ('Europe', 'Andorra la Vella'),
              'Afghanistan': ('Asia', 'Kabul'),
              'Antigua and Barbuda': ('North America', "St. John's"),
              'Albania': ('Europe', 'Tirana'),
              'Armenia': ('Asia', 'Yerevan'),
              'Angola': ('Africa', 'Luanda'),
              'Argentina': ('South America', 'Buenos Aires'),
              'Austria': ('Europe', 'Vienna'),
              'Australia': ('Oceania', 'Canberra'),
              'Azerbaijan': ('Asia', 'Baku'),
              'Barbados': ('North America', 'Bridgetown'),
              'Bangladesh': ('Asia', 'Dhaka'),
              'Belgium': ('Europe', 'Brussels')}

d = defaultdict(list)
for k,v in countries_dict.items():
  d[v[0]].append(k)
print(d)

输出

defaultdict(<class 'list'>, {'Europe': ['Andorra', 'Albania', 'Austria', 'Belgium'], 'Asia': ['Afghanistan', 'Armenia', 'Azerbaijan', 'Bangladesh'], 'North America': ['Antigua and Barbuda', 'Barbados'], 'Africa': ['Angola'], 'South America': ['Argentina'], 'Oceania': ['Australia']})

Answer 2

您可以在这里使用collections.defaultdict

def reverse_dict(countries_dict):
    reversed_dictionary  = defaultdict(list)
    for key, value in countries_dict.items():
        reversed_dictionary[value[0]].append(key)
    return reversed_dictionary

>>> reverse_dict(countries_dict)
defaultdict(<class 'list'>,
            {'Europe': ['Andorra', 'Albania', 'Austria', 'Belgium'],
             'Asia': ['Afghanistan', 'Armenia', 'Azerbaijan', 'Bangladesh'],
             'North America': ['Antigua and Barbuda', 'Barbados'],
             'Africa': ['Angola'],
             'South America': ['Argentina'],
             'Oceania': ['Australia']})

Answer 3

您可以将dict.setdefault()与默认列表（[]）一起使用，然后将国家/地区附加到其中：

out = {}
for country, (continent, _) in countries_dict.items():
    out.setdefault(continent, []).append(country)

print(out)

印刷品：

{'Europe': ['Andorra', 'Albania', 'Austria', 'Belgium'], 
 'Asia': ['Afghanistan', 'Armenia', 'Azerbaijan', 'Bangladesh'], 
 'North America': ['Antigua and Barbuda', 'Barbados'], 
 'Africa': ['Angola'], 
 'South America': ['Argentina'], 
 'Oceania': ['Australia']}