Python – Sum of different length Lists of list

Getting the sum of list is quite common problem and has been dealt with and discussed many times, but sometimes, we require to better it and total sum, i.e. including those of nested list as well. Let’s try and get the total sum and solve this particular problem. 

Method #1 : Using list comprehension + sum() We can solve this problem using the list comprehension as a potential shorthand to the conventional loops that we may use to perform this particular task. We just iterate and sum the nested list and at end return the cumulative sum using sum function. 

Python3

# Python3 code to demonstrate
# Sum of Uneven Lists of list
# Using list comprehension + sum()

# initializing list
test_list = [[1, 4, 5], [7, 3], [4], [46, 7, 3]]

# printing original list
print("The original list : " + str(test_list))

# using list comprehension + sum()
# Sum of Uneven Lists of list
res = sum([ele for sub in test_list for ele in sub])

# print result
print("The total element sum in lists is : " + str(res))

Output : 

The original list : [[1, 4, 5], [7, 3], [4], [46, 7, 3]]
The total element sum in lists is : 80

Time Complexity: O(n),The above code iterates through the list once, hence the time complexity is linear, i.e. O(n).
Space Complexity: O(n),The algorithm uses an additional list to store the result, thus consuming linear space which is O(n).

Method #2 : Using chain() + sum() This particular problem can also be solved using the chain function instead of list comprehension in which we use the conventional sum function to check the sum. 

Python3

# Python3 code to demonstrate
# Sum of Uneven Lists of list
# Using chain() + sum()
from itertools import chain

# initializing list
test_list = [[1, 4, 5], [7, 3], [4], [46, 7, 3]]

# printing original list
print("The original list : " + str(test_list))

# using chain() + sum()
# Sum of Uneven Lists of list
res = sum(list(chain(*test_list)))

# print result
print("The total element sum in lists is : " + str(res))

Output : 

The original list : [[1, 4, 5], [7, 3], [4], [46, 7, 3]]
The total element sum in lists is : 80

Method #3 : Using numpy.sum() and numpy.flatten()

Note: Install numpy module using command “pip install numpy”

Python3

import numpy as np

# initializing list
test_list = [[1, 4, 5], [7, 3], [4], [46, 7, 3]]

# printing original list
print("The original list : " + str(test_list))

# Using numpy.concatenate() and numpy.sum()
res = np.sum(np.concatenate([np.array(sublist) for sublist in test_list]))

# print result
print("The total element sum in lists is : " + str(res))
#This code is contributed by Edula Vinay Kumar Reddy

Output:

The original list : [[1, 4, 5], [7, 3], [4], [46, 7, 3]]
The total element sum in lists is : 80

Time Complexity: O(n) where n is the total number of elements in the nested list
Auxiliary Space : O(n) for storing the concatenated array.