Python – Maximum sum of elements of list in a list of lists

In this problem, we need to find the maximum sum of elements in a list of lists. A list of lists is a collection of sub-lists and each sub-list contains individual elements. The problem is to find the maximum sum among all the sub-lists. Let’s explore various ways to solve this problem.

Using sum() with max()

The simplest and most efficient way is by using the sum() function to calculate the sum of elements in each sub-list and then using the max() function to find the maximum sum.

# Input list of lists
lst = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

# Find the maximum sum of elements in the sub-lists
res = max(sum(sub_lst) for sub_lst in lst)
print(res)  

24

Explanation:

• sum() function is used to calculate the sum of elements in each sub-list.
• max() function is then used to find the sub-list with the highest sum.

Let’s explore some more ways and see how we can find the maximum sum of elements of list in a list of lists.

Using for loop

We can also use a for loop to iterate through each sub-list, calculate the sum of each sub-list and then keep track of the maximum sum encountered during the iteration.

# Input list of lists
a = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

# Initialize the maximum sum as a very small number
max_sum = float('-inf')

# Loop through each sub-list and calculate the sum
for b in a:
    cur_sum = sum(b)
    max_sum = max(max_sum, cur_sum)

print(max_sum) 

24

Explanation:

• We use a for loop to calculate the sum of each sub-list using the sum() function.
• We keep track of the maximum sum encountered so far using the max() function.

Using list comprehension and max()

This method is similar to the first one, but we will use list comprehension to create a list of sums and then apply the max() function to find the maximum sum.

a = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

# Create a list of sums and find the maximum sum
res = max([sum(sub_lst) for sub_lst in a])
print(res) 

24

Explanation:

• List comprehension is used to create a list of sums for each sub-list.
• max() function is then used to find the maximum sum from the list of sums.

Using numpy for large lists

If we are working with large lists, the numpy library can provide an efficient solution for this problem. Using numpy’s sum() function, we can find the maximum sum of elements in the list of lists.

import numpy as np
a = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

# Convert the list of lists to a numpy array
arr = np.array(a)

# Find the maximum sum of elements in a row (sub-list)
res = np.max(np.sum(arr, axis=1))
print(res)

24

Explanation:

• We first convert the list of lists into a numpy array.
• The np.sum() function calculates the sum of each row (sub-list) and np.max() finds the maximum sum.