Lets say I have the following list:
a = [[1,2,3],[4,5,6],[7,8,9]]
Is there a way to sum all the seconds elements without using loop? Such as:
the_sum = 0
for num in a:
the_sum += num[1]
>>> 15
4 Answers
Without using loop you can use zip() function:
>>> sum(list(zip(*a))[1])
15
Note: If you are using python 2.X since zip returns a list instead of an iterator you don't need to use list() on zip function.
Comments
Comprehensions:
a = [[1,2,3],[4,5,6],[7,8,9]]
print(sum(sublist[1] for sublist in a))
will result in
15
Comments
Use reduce so you dont create intermediate objects in memory:
>>>from functools import reduce
>>>reduce(lambda x, y: x + y[1], a, 0)
>>>15
Comments
All the other answers are totally fine, but here's a fourth way:
>>> import operator
>>> sum(map(operator.itemgetter(2), a))
15
sum([x[1] for x in a])(you know there is a loop here, but you can't see it).