Summing up the elements of lists in a for loop

Question

So the basis of my question is given here. After all I need to add elements of the lists. In the simplest example:

first = [1,2]
second = [6,7]

Then

[x + y for x, y in zip(first, second)]

which gives:

#[7,9]

However my problem is that I am producing number of lists via a for loop. In the for loop the lists are not being stored and so to see them one uses print(list) at the end of the loop and it prints the lists. Now how can I write a code to look at the produced lists and sum the elements in the given manner above?

Example:

l = []
for i in range(2):
    l= list(range(5))
    print(l)

the above produces:

#[0, 1, 2, 3, 4]
#[0, 1, 2, 3, 4]

How can I add a line in the for loop to sum the one-by-one elements of the lists to get:

#[0, 2, 4, 6, 8]

post the code that produces the lists please. This is hard to understand as it is. — Ma0, Apr 26 '18 at 09:19
If the lists are only printed and not stored, then you can't use them later. — Aran-Fey, Apr 26 '18 at 09:22
@Will As Aran said, you cannot use what you do not store and in your case, `l` is being overwritten and thus, the old is gone. — Ma0, Apr 26 '18 at 09:25
@Aran-Fey How do you store? I have added an example of the problem which would help. — Will, Apr 26 '18 at 09:25

score 1 · Accepted Answer · answered Apr 26 '18 at 09:31

Use a variable to hold the totals, and update it in the loop

totals = [0]*5
for i in range(5):
    l = list(range(5))
    totals = [x + y for x, y in zip(totals, l)]
print totals

Or you can save all your lists in another list, and then use your original idea:

all_lists = []
for i in range(5):
    l = list(range(5))
    all_lists.append(l)
totals = [sum(lists) for lists in zip(*all_lists)]

score 0 · Answer 2 · answered Apr 26 '18 at 09:39

0

From what I understand, here is another way of doing it i.e. using operator add.

from operator import add
n=5
l = [0]*n
for i in range(2):
    l = map(add, l, range(n))

print([x for x in l])

Output:

[0, 2, 4, 6, 8]

answered Apr 26 '18 at 09:39

Sumit Jha

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Summing up the elements of lists in a for loop

2 Answers2