[英]Check how many items from one list appear in another list
If I have 2 lists, for an example:例如,如果我有 2 个列表:
list_1 = ['a', 'A']
list_2 = ['a', 'A', 'A', 'b', 'b', 'b', 'b']
How can I make a count to see how many times the items from list_1
appear in list_2
?如何计数以查看list_1
中的项目出现在list_2
中的次数?
So in this case it should return 3
.所以在这种情况下它应该返回3
。
list_1 = ['a', 'A']
list_2 = ['a', 'A', 'A', 'b', 'b', 'b', 'b']
found = 0
for x in list_1:
for y in list_2:
if x == y:
found += 1
print(found)
An efficient O(n) method using a set as reference:使用集合作为参考的有效 O(n) 方法:
list_1 = ['a', 'A']
list_2 = ['a', 'A', 'A', 'b', 'b', 'b', 'b']
set_1 = set(list_1)
count = 0
for e in list_2:
if e in set_1:
counter += 1
Output: 3
Output: 3
A one liner:一个班轮:
sum([x == y for x in list_1 for y in list_2])
Another solution, which could be beneficial in other cases, because the Counter()- object returns a dictionary with the already summed up elements另一种解决方案,在其他情况下可能是有益的,因为 Counter()- object 返回一个包含已汇总元素的字典
from collections import Counter
list_1 = ['a', 'A']
list_2 = ['a', 'A', 'A', 'b', 'b', 'b', 'b']
c = Counter(list_2)
print(sum([c[x] for x in list_1]))
Just use count for lists:只需对列表使用计数:
print(list_2.count(list_1[0]) + list_2.count(list_1[1]))
or in a loop:或循环:
sum_ = 0
for i in range(len(list_1)):
sum_ += list_2.count(list_1[i])
print(sum_)
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