Print diagonals of 2d list in Python

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In this tutorial, you will learn how to print diagonals of 2d list in Python.

To print the diagonals of a 2d list in Python, we need to iterate through the elements of the diagonals and collect them into a list.

As all the diagonal elements have the same row number and column number we need to identify those elements and print those elements which become the diagonals of the list.

Here’s a step-by-step procedure to do this:

1. Identify the Diagonals of the 2d list:

The main diagonal of the matrix consists of the same row number and column number(For example: [0][0], [1][1], [2][2], etc).

2. Initialize the Matrix:

Initialize a 2 dimensional matrix to work with

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

3. Determine the Size of the Matrix:

To handle the matrices that have different number of rows and columns, find the minimum dimension

size=min(len(m), len(m[0]))

This makes sure that when you access the diagonal elements, you do not go out of bounds

4. Retrieve the Diagonal Elements:

Collect the elements where the row index is equal to the column index using the List comprehension

diagonal=[m[i][i] for i in range (size)]

This iterates from the first element i.e., [0] to the last element i.e., [n-1].

For example: It will pick the elements such as m[0][0], m[1][1], m[2][2], etc.

5. Print the Diagonal Elements of the 2d Matrix:

Now, print the elements that are collected

print("Diagonal elements of the Matrix are:", diagonal)

Complete code:

def print_diagonal(m):
    size = min(len(m), len(m[0]))
    diagonal = [m[i][i] for i in range(size)]
    print("Diagonal elements of the Matrix are:", diagonal)
    

# Example 
m = [
    [1, 2, 3],
    [4, 5, 6],
    [7, 8, 9]
]

print_diagonal(m)

Output:

Diagonal elements of the Matrix are: [1, 5, 9]

The diagonals of a 2d matrix can be easily retrieved and printed using this simple and straightforward approach.

This is an additional example of learning this problem

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