python：翻译频率图列表的快速方法

Question

[“ A”，“ A”，“ A”，“ B”，“ B”，“ B”]的列表

的词典 {'A'：3，  'B'：3}

我已经做了下面的事情，但是我感觉有更快/更短的方法吗？

frequencyMap = dict()
letters = ["A","A","A","B","B","B"]

for letter in letters:
    if letter not in frequencyMap:
        frequencyMap[letter] = 0
    frequencyMap[letter] += 1

Answer 1

在Python 2.7（或更高版本）中，您可以使用collections.Counter

collections.Counter（）

计数器是一个将元素存储为字典键的容器，它们的计数存储为字典值。

import collections
a = [1,1,1,1,2,2,2,2,3,3,4,5,5]
counter=collections.Counter(a)
print(counter)
# Counter({1: 4, 2: 4, 3: 2, 5: 2, 4: 1})

Answer 2

from collections import Counter

print(Counter(["A","A","A","B","B","B"]))