Python | Column wise sum of nested list

Given a nested list (where sublists are of equal length), write a Python program to find the column-wise sum of the given list and return it in a new list.

Examples:

Input : [[1, 5, 3],
         [2, 7, 8],
         [4, 6, 9]]
Output : [7, 18, 20]

Input : [[20, 5],
         [2, 54],
         [45, 9], 
         [72, 3]]
Output : [139, 71]

Method #1 : zip using list comprehension

We can find sum of each column of the given nested list using zip function of python enclosing it within list comprehension.

# Python3 program to Column wise sum of nested list

def column_sum(lst):

     return [sum(i) for i in zip(*lst)]

# Driver code
lst = [[1, 5, 3], [2, 7, 8], [4, 6, 9]]
print(column_sum(lst))

Output:

[7, 18, 20]

Method #2 : Using map() method

Another approach is to use map(). We apply the sum function to each element in a column and find sum of each column accordingly.

# Python3 program to Column wise sum of nested list

def column_sum(lst):

    return list(map(sum, zip(*lst)))

# Driver code
lst = [[1, 5, 3], [2, 7, 8], [4, 6, 9]]
print(column_sum(lst))

Output:

[7, 18, 20]

Method #3 : Using numpy.sum()

numpy.sum() function returns the sum of array elements over the specified axis.

# Python3 program to Column wise sum of nested list
from numpy import array

def column_sum(lst):
    arr = array(lst)
    return sum(arr, 0).tolist()

# Driver code
lst = [[1, 5, 3], [2, 7, 8], [4, 6, 9]]
print(column_sum(lst))

Output:

[7, 18, 20]