Python program to sort matrix based upon sum of rows

When it is required to sort a matrix based upon the sum of rows, we can use Python's built-in sort() method with a custom key function. The key function calculates the sum of each row, and the matrix is sorted in ascending order based on these sums.

Method 1: Using a Custom Function

Define a helper function that calculates the sum of a row and use it as the key for sorting ?

def sort_sum(row):
    return sum(row)

matrix = [[34, 51], [32, 15, 67], [12, 41], [54, 36, 22]]

print("The matrix is :")
print(matrix)

matrix.sort(key=sort_sum)

print("The sorted matrix is :")
print(matrix)

The matrix is :
[[34, 51], [32, 15, 67], [12, 41], [54, 36, 22]]
The sorted matrix is :
[[12, 41], [34, 51], [54, 36, 22], [32, 15, 67]]

Method 2: Using Lambda Function

A more concise approach using a lambda function ?

matrix = [[34, 51], [32, 15, 67], [12, 41], [54, 36, 22]]

print("Original matrix:")
print(matrix)

matrix.sort(key=lambda row: sum(row))

print("Sorted matrix:")
print(matrix)

Original matrix:
[[34, 51], [32, 15, 67], [12, 41], [54, 36, 22]]
Sorted matrix:
[[12, 41], [34, 51], [54, 36, 22], [32, 15, 67]]

Method 3: Using sorted() Function

If you want to keep the original matrix unchanged, use sorted() which returns a new sorted list ?

matrix = [[34, 51], [32, 15, 67], [12, 41], [54, 36, 22]]

print("Original matrix:")
print(matrix)

sorted_matrix = sorted(matrix, key=sum)

print("Sorted matrix:")
print(sorted_matrix)

print("Original matrix remains unchanged:")
print(matrix)

Original matrix:
[[34, 51], [32, 15, 67], [12, 41], [54, 36, 22]]
Sorted matrix:
[[12, 41], [34, 51], [54, 36, 22], [32, 15, 67]]
Original matrix remains unchanged:
[[34, 51], [32, 15, 67], [12, 41], [54, 36, 22]]

How It Works

The sorting is based on row sums:

• [12, 41] ? sum = 53 (smallest)

• [34, 51] ? sum = 85

• [54, 36, 22] ? sum = 112

• [32, 15, 67] ? sum = 114 (largest)

Comparison

Conclusion

Use sort(key=sum) for in-place sorting or sorted(matrix, key=sum) to preserve the original matrix. The sum function works directly as a key since it calculates the total of each row.