Python：有效計算字典列表中鍵的唯一值的數量

Question

必須有一個更好的方法來編寫這個Python代碼，我有一個人的列表（人們是字典），我試圖找到某個鍵​​的唯一值的數量（在這種情況下，鍵稱為國籍，我是試圖找到人名單中的獨特國籍數量）：

no_of_nationalities = []
for p in people:
    no_of_nationalities.append(p['Nationality'])
print 'There are', len(set(no_of_nationalities)), 'nationalities in this list.'

非常感謝

Answer 1

更好的方法是直接從字典構建set ：

print len(set(p['Nationality'] for p in people))

Answer 2

有collections模塊

import collections
....
count = collections.Counter()
for p in people:
    count[p['Nationality']] += 1;
print 'There are', len(count), 'nationalities in this list.'

這樣你就可以統計每個國籍。

print(count.most_common(16))#print 16 most frequent nationalities 

Answer 3

count = len(set(p['Nationality'] for p in people))
print 'There are' + str(count) + 'nationalities in this list.'

Answer 4

len(set(x['Nationality'] for x in p))