How to sum lists together in python

The zip function is useful here, used with a list comprehension.

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

If you have a list of lists [instead of just two lists]:

lists_of_lists = [[1, 2, 3], [4, 5, 6]]
[sum[x] for x in zip[*lists_of_lists]]
# -> [5, 7, 9]

answered Dec 27, 2012 at 7:12

8

From docs

import operator
list[map[operator.add, first,second]]

answered Dec 27, 2012 at 7:29

Thai TranThai Tran

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1

Default behavior in numpy.add [numpy.subtract, etc] is element-wise:

import numpy as np
np.add[first, second]

which outputs

array[[7,9,11,13,15]]

mirekphd

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answered Apr 28, 2014 at 19:57

user3582790user3582790

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7

Assuming both lists a and b have same length, you do not need zip, numpy or anything else.

Python 2.x and 3.x:

[a[i]+b[i] for i in range[len[a]]]

maro

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answered Jun 30, 2014 at 15:31

mathmath

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1

Try the following code:

first = [1, 2, 3, 4]
second = [2, 3, 4, 5]
third = map[sum, zip[first, second]]

kenorb

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answered May 16, 2015 at 12:45

1

This extends itself to any number of lists:

[sum[sublist] for sublist in itertools.izip[*myListOfLists]]

In your case, myListOfLists would be [first, second]

answered Dec 27, 2012 at 7:20

inspectorG4dgetinspectorG4dget

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2

The easy way and fast way to do this is:

three = [sum[i] for i in zip[first,second]] # [7,9,11,13,15]

Alternatively, you can use numpy sum:

from numpy import sum
three = sum[[first,second], axis=0] # array[[7,9,11,13,15]]

answered Mar 17, 2013 at 9:25

ThiruThiru

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1

one-liner solution

list[map[lambda x,y: x+y, a,b]]

answered Jul 25, 2019 at 7:36

ShadowmanShadowman

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first = [1, 2, 3, 4, 5]
second = [6, 7, 8, 9, 10]
three = list[map[sum, first, second]]
print[three]



# Output 
[7, 9, 11, 13, 15]

KetZoomer

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answered Jul 21, 2017 at 8:11

Anurag MisraAnurag Misra

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1

If you have an unknown number of lists of the same length, you can use the below function.

Here the *args accepts a variable number of list arguments [but only sums the same number of elements in each]. The * is used again to unpack the elements in each of the lists.

def sum_lists[*args]:
    return list[map[sum, zip[*args]]]

a = [1,2,3]
b = [1,2,3]  

sum_lists[a,b]

Output:

[2, 4, 6]

Or with 3 lists

sum_lists[[5,5,5,5,5], [10,10,10,10,10], [4,4,4,4,4]]

Output:

[19, 19, 19, 19, 19]

answered May 19, 2019 at 13:44

0

My answer is repeated with Thiru's that answered it in Mar 17 at 9:25.

It was simpler and quicker, here are his solutions:

The easy way and fast way to do this is:

 three = [sum[i] for i in zip[first,second]] # [7,9,11,13,15]

Alternatively, you can use numpy sum:

 from numpy import sum
 three = sum[[first,second], axis=0] # array[[7,9,11,13,15]]

You need numpy!

numpy array could do some operation like vectors

import numpy as np
a = [1,2,3,4,5]
b = [6,7,8,9,10]
c = list[np.array[a] + np.array[b]]
print c
# [7, 9, 11, 13, 15]

answered Oct 22, 2013 at 9:58

PiecePiece

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1

What if you have list with different length, then you can try something like this [using zip_longest]

from itertools import zip_longest  # izip_longest for python2.x

l1 = [1, 2, 3]
l2 = [4, 5, 6, 7]

>>> list[map[sum, zip_longest[l1, l2, fillvalue=0]]]
[5, 7, 9, 7]

answered Apr 26, 2020 at 19:21

mohammed wazeemmohammed wazeem

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You can use zip[], which will "interleave" the two arrays together, and then map[], which will apply a function to each element in an iterable:

>>> a = [1,2,3,4,5]
>>> b = [6,7,8,9,10]
>>> zip[a, b]
[[1, 6], [2, 7], [3, 8], [4, 9], [5, 10]]
>>> map[lambda x: x[0] + x[1], zip[a, b]]
[7, 9, 11, 13, 15]

answered Dec 27, 2012 at 7:12

cdhowiecdhowie

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Here is another way to do it. We make use of the internal __add__ function of python:

class SumList[object]:
    def __init__[self, this_list]:
        self.mylist = this_list

    def __add__[self, other]:
        new_list = []
        zipped_list = zip[self.mylist, other.mylist]
        for item in zipped_list:
            new_list.append[item[0] + item[1]]
        return SumList[new_list]

    def __repr__[self]:
        return str[self.mylist]

list1 = SumList[[1,2,3,4,5]]
list2 = SumList[[10,20,30,40,50]]
sum_list1_list2 = list1 + list2
print[sum_list1_list2]

Output

[11, 22, 33, 44, 55]

TrakJohnson

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answered Sep 23, 2016 at 19:18

StrykerStryker

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If you want to add also the rest of the values in the lists you can use this [this is working in Python3.5]

def addVectors[v1, v2]:
    sum = [x + y for x, y in zip[v1, v2]]
    if not len[v1] >= len[v2]:
        sum += v2[len[v1]:]
    else:
        sum += v1[len[v2]:]

    return sum


#for testing 
if __name__=='__main__':
    a = [1, 2]
    b = [1, 2, 3, 4]
    print[a]
    print[b]
    print[addVectors[a,b]]

answered May 10, 2017 at 10:59

    first = [1,2,3,4,5]
    second = [6,7,8,9,10]
    #one way
    third = [x + y for x, y in zip[first, second]]
    print["third" , third] 
    #otherway
    fourth = []
    for i,j in zip[first,second]:
        global fourth
        fourth.append[i + j]
    print["fourth" , fourth ]
#third [7, 9, 11, 13, 15]
#fourth [7, 9, 11, 13, 15]

answered Jul 5, 2017 at 11:49

Here is another way to do it.It is working fine for me .

N=int[input[]]
num1 = list[map[int, input[].split[]]]
num2 = list[map[int, input[].split[]]]
sum=[]

for i in range[0,N]:
  sum.append[num1[i]+num2[i]]

for element in sum:
  print[element, end=" "]

print[""]

Agney

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answered Sep 11, 2017 at 19:49

j = min[len[l1], len[l2]]
l3 = [l1[i]+l2[i] for i in range[j]]

Cris Luengo

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answered Dec 27, 2017 at 5:06

1

If you consider your lists as numpy array, then you need to easily sum them:

import numpy as np

third = np.array[first] + np.array[second]

print third

[7, 9, 11, 13, 15]

answered Apr 25, 2019 at 10:32

RadvinRadvin

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Perhaps the simplest approach:

first = [1,2,3,4,5]
second = [6,7,8,9,10]
three=[]

for i in range[0,5]:
    three.append[first[i]+second[i]]

print[three]

answered Jul 26, 2018 at 15:20

first = [1,2,3,4,5]
second = [6,7,8,9,10]
third=[]
for i,j in zip[first,second]:
    t=i+j
    third.append[t]
print["Third List=",third]

output -- Third List= [7, 9, 11, 13, 15]

answered Sep 13 at 7:51

2

You can use this method but it will work only if both the list are of the same size:

first = [1, 2, 3, 4, 5]
second = [6, 7, 8, 9, 10]
third = []

a = len[first]
b = int[0]
while True:
    x = first[b]
    y = second[b]
    ans = x + y
    third.append[ans]
    b = b + 1
    if b == a:
        break

print third

answered Dec 27, 2012 at 11:52

HelloUniHelloUni

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