I have the following two lists:
first = [1,2,3,4,5] second = [6,7,8,9,10] Now I want to add the items from both of these lists into a new list.
output should be
third = [7,9,11,13,15] 21 Answers
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] From docs
import operator list(map(operator.add, first,second)) 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]) 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))] Try the following code:
first = [1, 2, 3, 4] second = [2, 3, 4, 5] third = map(sum, zip(first, second)) This extends itself to any number of lists:
[sum(sublist) for sublist in itertools.izip(*myListOfLists)] In your case, myListOfLists would be [first, second]
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]) one-liner solution
list(map(lambda x,y: x+y, a,b)) 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] 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] 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] 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] 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] 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] 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)) 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] 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("") j = min(len(l1), len(l2)) l3 = [l1[i]+l2[i] for i in range(j)] 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] 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) 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 
