python 统计列表中元素出现的次数

from collections import Counter
import numpy as np


l = ['a', 'b', 'c', 'd', 'a', 'v', 's', 'd', 'c', 'a']

# 最简单的 Counter 计数法
print(Counter(l).most_common(2))

# 正常写法先 set 后统计
res = {}
for i in set(l):
    res[i] = l.count(i)
print(res)

# 比较骚的 numpy 计数
arr = np.array(l)
key = np.unique(l)
result = {}
for k in key:
    mask = (arr == k)
    arr_new = arr[mask]
    v = arr_new.size
    result[k] = v
print(result)