NumPy: Rearrange columns of a given numpy 2D array using given index positions

Last update on August 29 2025 12:46:08 (UTC/GMT +8 hours)

Rearrange columns of a 2D array using indices.

Write a NumPy program to rearrange columns of a given numpy 2D array using given index positions.

Sample Solution:

Python Code:

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

# Creating a NumPy array
array1 = np.array([[11, 22, 33, 44, 55],
                    [66, 77, 88, 99, 100]])

# Displaying the original array
print("Original arrays:")
print(array1)

# Creating a list of indices for reordering columns
i = [1, 3, 0, 4, 2]

# Rearranging the columns of the original array based on the given indices
result = array1[:, i]

# Displaying the new array formed by rearranging columns
print("New array:")
print(result)

Sample Output:

Original arrays:
[[ 11  22  33  44  55]
 [ 66  77  88  99 100]]
New array:
[[ 22  44  11  55  33]
 [ 77  99  66 100  88]]

Explanation:

In the above exercise -

• array1 = np.array([[11, 22, 33, 44, 55], [66, 77, 88, 99, 100]]): Create a 2D NumPy array with given values.
• i: Define a list of column indices representing the desired order of columns.
• array1[:,i]: Rearrange the columns of array1 according to the specified order in i. Here, the colon : means to select all rows and ‘i’ is the list of column indices in the desired order.
• result: Store the resulting NumPy array.

Pictorial Presentation:

For more Practice: Solve these Related Problems:

• Write a NumPy program to rearrange the columns of a 2D array according to a given permutation of indices using advanced indexing.
• Create a function that accepts a 2D array and a list of column indices, then returns the array with rearranged columns.
• Implement a solution that uses np.take along axis 1 to reorder the columns based on a provided index array.
• Test the column rearrangement on matrices with duplicate and unsorted indices to verify correct ordering.

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