计算两个列表中的频率,Python

Question

我是python编程的新手,所以请关注我的新手问题......

我有一个初始列表(list1),我已经清理了重复项,最后只有一个列表,每个值只有一个(list2):

list1 = [13,19,13,2,16,6,5,19,20,21,20,13,19,13,16],

list2 = [13,19,2,16,6,5,20,21]

我想要的是计算"list2"中每个值出现在"list1"中的次数,但我无法弄清楚如何做到这一点而不会出错.

我正在寻找的输出类似于:

数字13在list1中表示1次.........数字16在list1中表示2次.

Answer 1

visited = []
for i in list2:
  if i not in visited:
    print "Number", i, "is presented", list1.count(i), "times in list1"
    visited.append(i)

Answer 2

最简单的方法是使用计数器:

from collections import Counter
list1 = [13, 19, 13, 2, 16, 6, 5, 19, 20, 21, 20, 13, 19, 13, 16]
c = Counter(list1)
print(c)

给

Counter({2: 1, 5: 1, 6: 1, 13: 4, 16: 2, 19: 3, 20: 2, 21: 1})

因此,您可以使用与访问dicts相同的语法来访问表示项目及其出现次数的计数器的键值对:

for k, v in c.items():
    print('- Element {} has {} occurrences'.format(k, v))

赠送:

- Element 16 has 2 occurrences
- Element 2 has 1 occurrences
- Element 19 has 3 occurrences
- Element 20 has 2 occurrences
- Element 5 has 1 occurrences
- Element 6 has 1 occurrences
- Element 13 has 4 occurrences
- Element 21 has 1 occurrences