Python:如何在三个列表中找到公共值 [英] Python: how to find common values in three lists

问题描述

我尝试为三个不同的列表找到共同的值列表:

a = [1,2,3,4]b = [2,3,4,5]c = [3,4,5,6]

当然，我尝试使用 and 运算符，但是这样我只会得到表达式中最后一个 list 的值:

<代码>>>a 和 b 和 c出:[3,4,5,6]

有没有找到通用值列表的捷径:

[3,4]

Br

解决方案

使用集合:

<预><代码>>>>a = [1, 2, 3, 4]>>>b = [2, 3, 4, 5]>>>c = [3, 4, 5, 6]>>>设置(a) &设置(b) &设置(c){3, 4}

或者像乔恩建议的那样:

<预><代码>>>>设置(a).交集(b，c){3, 4}

使用集合的好处是不需要重复迭代原始列表.每个列表迭代一次以创建集合，然后将集合相交.

像 Geotob 那样使用过滤列表推导式来解决这个问题的天真方法是为 a 的每个元素迭代列表 b 和 c，所以对于更长的列表，这会降低很多效率.

I try to find common list of values for three different lists:

a = [1,2,3,4]
b = [2,3,4,5]
c = [3,4,5,6]

of course naturally I try to use the and operator however that way I just get the value of last list in expression:

>> a and b and c
out: [3,4,5,6]

Is any short way to find the common values list:

[3,4]

Br

解决方案

Use sets:

>>> a = [1, 2, 3, 4]
>>> b = [2, 3, 4, 5]
>>> c = [3, 4, 5, 6]
>>> set(a) & set(b) & set(c)
{3, 4}

Or as Jon suggested:

>>> set(a).intersection(b, c)
{3, 4}

Using sets has the benefit that you don’t need to repeatedly iterate the original lists. Each list is iterated once to create the sets, and then the sets are intersected.

The naive way to solve this using a filtered list comprehension as Geotob did will iterate lists b and c for each element of a, so for longer list, this will be a lot less efficient.

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