CODEWITHSUNDEEP
pythonlist2delement
sari023
sari023

Reputation: 15

Adding each element in a 2d list to another 2d list in Python

So i need to define a function, in which i get 2 lists that are 2d. The goal is to add each element to each other.


list1 = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
list2 = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

the result should be this:

   result = [[2,4,6], [8,10,12],[14,16,18]]

So far, i built this function:

def add_matrices(list1, list2):
    matrix = list1 + list2
    return matrix

But im kinda stuck now, I have tried to use append and extend, but both didn't work. I have found a few solutions that required the usage of numpy, which unfortunately isn't allowed for this. Can anybody please guide me in the right direction?

Upvotes: 0

Views: 458

Answers (1)

Dani Mesejo
Dani Mesejo

Reputation: 61920

One approach:

list1 = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
list2 = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]


res = [[e1 + e2 for e1, e2 in zip(li1, li2)] for li1, li2 in zip(list1, list2)]
print(res)

Output

[[2, 4, 6], [8, 10, 12], [14, 16, 18]]

Functional alternative using map:

from operator import add
res = [list(map(add, li1, li2)) for li1, li2 in zip(list1, list2)]
print(res)

UPDATE

If required to return None if any of the inner list do not match in length, do the following:

list1 = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
list2 = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]


def list_sum(lst1, lst2):
    if any(len(e1) != len(e2) for e1, e2 in zip(lst1, lst2)):
        return None
    return [[e1 + e2 for e1, e2 in zip(li1, li2)] for li1, li2 in zip(list1, list2)]


print(list_sum(list1, list2))
print(list_sum([[1, 2], [4, 5], [7, 8]], [[1, 2, 3], [4, 5, 6], [7, 8, 9]]))

Output

[[2, 4, 6], [8, 10, 12], [14, 16, 18]]
None

Upvotes: 2

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