问题描述
在传统的python中，sum函数给出一个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，如果你有一个嵌套列表怎么办:
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
要获得所有第一个元素的总和，您需要有一个生成器表达式
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
您得到 unsupported operand type(s) for +: 'int' and 'list' 因为您尝试添加三个列表，这不是所需的行为.
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.
如果您想要一个第一个元素的列表，然后找到它们的总和，您可以尝试使用列表推导
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 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跟版网！