嵌套列表中的第一个值的总和

问题描述

在传统的python中，sum函数给出list的总和:

In traditional python, the sum function gives the sum of a list:

sum([0,1,2,3,4])=10

另一方面，如果您有嵌套列表，该怎么办:

On the other hand, what if you have a nested list as so:

sum([[1,2,3],[4,5,6],[7,8,9]])

我们发现了错误:

Traceback (most recent call last):
  File "<input>", line 1, in <module>
TypeError: unsupported operand type(s) for +: 'int' and 'list'

除此之外，我们如何在嵌套列表中找到第一个值(索引0)的sum?如:

In addition to this, how could we find the sum of the first values (index 0) in a nested list? Such as:

something([[1,2,3],[4,5,6],[7,8,9]])=12

推荐答案

要获取所有第一个元素的总和，您需要具有生成器表达式

To get the sum of all the first elements you need to have a generator expression

>>> a = [[1,2,3],[4,5,6],[7,8,9]]
>>> sum(i[0] for i in a)
12

之所以得到unsupported operand type(s) for +: 'int' and 'list'，是因为您试图添加这三个列表，这不是您想要的行为.

You are getting unsupported operand type(s) for +: 'int' and 'list' because you are trying to add the three lists which is not the desired behavior.

如果要先列出一个元素然后找到它们的总和，则可以尝试使用列表理解

If you want a list of first elements and then find their sum, you can try a list comprehension instead

>>> l = [i[0] for i in a]
>>> l
[1, 4, 7]
>>> sum(l)
12

或者您可以调用__next__方法，因为列表是可迭代的(如果是Py3)

Or you can call the __next__ method as list is an iterable (If Py3)

>>> sum(zip(*a).__next__())
12

这篇关于嵌套列表中的第一个值的总和的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！