Element-wise addition of 2 lists?

Question

I have now:

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

I wish to have:

[1, 2, 3]
 +  +  +         


        

Answer 1

This is simple with numpy.add()

import numpy

list1 = numpy.array([1, 2, 3])
list2 = numpy.array([4, 5, 6])
result = numpy.add(list1, list2) # result receive element-wise addition of list1 and list2
print(result)
array([5, 7, 9])

See doc here

If you want to receiver a python list:

result.tolist()

Answer 2

This will work for 2 or more lists; iterating through the list of lists, but using numpy addition to deal with elements of each list

import numpy as np
list1=[1, 2, 3]
list2=[4, 5, 6]

lists = [list1, list2]
list_sum = np.zeros(len(list1))
for i in lists:
   list_sum += i
list_sum = list_sum.tolist()    

[5.0, 7.0, 9.0]

Answer 3

• The zip function is useful here, used with a list comprehension v1, v2.
• If you have a list of lists (instead of just two lists) you can use v3.
• For lists with different length (for example: By adding 1 to the end of the first/secound list), then you can try something like this (using zip_longest) - v4

first = [1, 2, 3, 1]
second = [4, 5, 6]

output: [5, 7, 9, 1]

• If you have an unknown number of lists of the same length, you can use the function v5.

• v6 - The operator module exports a set of efficient functions corresponding to the intrinsic operators of Python. For example, operator.add(x, y) is equivalent to the expression x+y.

• v7 - Assuming both lists first and second have same length, you do not need zip or anything else.

################
first = [1, 2, 3]
second = [4, 5, 6]

####### v1 ########
third1 = [sum(i) for i in zip(first,second)]

####### v2 ########
third2 = [x + y for x, y in zip(first, second)]

####### v3 ########
lists_of_lists = [[1, 2, 3], [4, 5, 6]]
third3 = [sum(x) for x in zip(*lists_of_lists)]

####### v4 ########
from itertools import zip_longest
third4 = list(map(sum, zip_longest(first, second, fillvalue=0)))

####### v5 ########
def sum_lists(*args):
    return list(map(sum, zip(*args)))

third5 = sum_lists(first, second)

####### v6 ########
import operator
third6 = list(map(operator.add, first,second))

####### v7 ########
third7 =[first[i]+second[i] for i in range(len(first))]

####### v(i) ########

print(third1) # [5, 7, 9]
print(third2) # [5, 7, 9]
print(third3) # [5, 7, 9]
print(third4) # [5, 7, 9]
print(third5) # [5, 7, 9]
print(third6) # [5, 7, 9]
print(third7) # [5, 7, 9]

Answer 4

Use map with lambda function:

>>> map(lambda x, y: x + y, list1, list2)
[5, 7, 9]