NumPy: Swap columns in a given array

Last update on August 29 2025 12:46:04 (UTC/GMT +8 hours)

Swap Columns in 2D Array

Write a NumPy program to swap columns in a given array.

Sample Solution:

Python Code:

# Importing the NumPy library and aliasing it as 'np'
import numpy as np

# Creating a NumPy array 'my_array' with elements from 0 to 11, reshaped into a 3x4 matrix
my_array = np.arange(12).reshape(3, 4)

# Displaying a message indicating the original array will be printed
print("Original array:")

# Printing the original array 'my_array'
print(my_array)

# Swapping columns 0 and 1 of the array using NumPy indexing
my_array[:, [0, 1]] = my_array[:, [1, 0]]

# Displaying a message indicating the array after swapping will be printed
print("\nAfter swapping arrays:")

# Printing the array after swapping columns 0 and 1
print(my_array)

Sample Output:

Original array:
[[ 0  1  2  3]
 [ 4  5  6  7]
 [ 8  9 10 11]]

After swapping arrays:
[[ 1  0  2  3]
 [ 5  4  6  7]
 [ 9  8 10 11]]

Explanation:

In the above exercise -

my_array = np.arange(12).reshape(3, 4): This line creates a 2-dimensional NumPy array called my_array with the shape (3, 4) and elements from 0 to 11.

my_array[:,[0, 1]] = my_array[:,[1, 0]]: This line swaps the first and second columns of my_array. The part my_array[:,[0, 1]] selects the first and second columns, while my_array[:,[1, 0]] selects the second and first columns, in that order. By assigning my_array[:,[1, 0]] to my_array[:,[0, 1]], the first and second columns are effectively swapped.

Finally print() function prints the resulting ‘my_array’ after swapping the columns.

Pictorial Presentation:

For more Practice: Solve these Related Problems:

Write a NumPy program to swap two specified columns in a 2D array using advanced indexing.
Create a function that accepts a 2D array and two column indices, then returns the array with those columns swapped.
Test the column swap on arrays with different data types and verify the order of elements post-swap.
Implement a solution that uses np.copy to avoid modifying the original array during the swap process.

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Python-Numpy Code Editor:

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