How can I add the corresponding elements of several lists of numbers?

Question

I have some lists of numbers:

[1, 2, 3, 4, 5]
[2, 3, 4, 5, 6]
[3, 4, 5, 6, 7]

How can I add these lists' elements, assuming that all of the lists that I'm using are the same length?

Here's the kind of output I'd like to get from doing this to the above lists.

[6, 9, 12, 15, 18]

I know that I'll need a loop of some kind - but how can I do it elegantly?

Answer 1

Try this functional style code:

>>> map(sum, zip(*lists))
[6, 9, 12, 15, 18]

The zip function matches elements with the same index.

>>> zip(*lists)
[(1, 2, 3), (2, 3, 4), (3, 4, 5), (4, 5, 6), (5, 6, 7)]

Then sum is applied to each tuple by using map.

See it working online: ideone

---

Note that in Python 3.x, map no longer returns a list. If you need the list, please see the following question:

• Getting a map() to return a list in Python 3.x

(You can just call list).

Answer 2

>>> lis=[[1,2,3,4,5],[2,3,4,5,6],[3,4,5,6,7]]

>>> [sum(x) for x in zip(*lis)]
[6, 9, 12, 15, 18]

Answer 3

Assuming:

a = [1,2,3,4,5]
b = [2,3,4,5,6]
c = [3,4,5,6,7]

just do this:

[sum(n) for n in zip(*[a, b, c])]

Answer 4

Using numpy:

>>> seq = np.array([
... [1,2,3,4,5],
... [2,3,4,5,6],
... [3,4,5,6,7]])
>>> np.sum(seq,axis=0)
array([ 6,  9, 12, 15, 18])

Answer 5

How about:

a = [1,2,3,4,5]
b = [2,3,4,5,6]
c = [3,4,5,6,7]

s = map(sum, zip(a,b,c))

Answer 6

This one works for lists with various length too(nested only 1 time).

def sum_list_of_list_of_int(ll):
    l=[]
    for i in ll:  # "i" type is list
        for ii in range(len(i)):  # "ii" type is int
            if len(l)-1>=ii:
                l[ii]+=int(i[ii])
            else:
                l.append(int(i[ii]))
    return l