title: frequencies
tags: list,intermediate
Returns a dictionary with the unique values of a list as keys and their frequencies as the values.
Use a for
loop to populate a dictionary, f
, with the unique values in lst
as keys, adding to existing keys every time the same value is encountered.
代码实现
from functools import reduce
def frequencies(lst):
f = {}
for x in lst:
f[x] = f[x] + 1 if x in f else 1
return f
使用样例
frequencies(['a', 'b', 'a', 'c', 'a', 'a', 'b']) # { 'a': 4, 'b': 2, 'c': 1 }