Index and select elements in 2D NumPy Array using Tuple of arrays

Last update on April 29 2025 13:01:45 (UTC/GMT +8 hours)

8. 2D Array & Tuple of Arrays Indexing

Indexing with a Tuple of Arrays:

Write a NumPy program that creates a 2D NumPy array and uses a tuple of arrays to index and select a specific set of elements.

Sample Solution:

Python Code:

import numpy as np

# Create a 2D NumPy array of shape (5, 5) with random integers
array_2d = np.random.randint(0, 100, size=(5, 5))

# Define row and column indices as a tuple of arrays
row_indices = np.array([0, 1, 2, 3])
col_indices = np.array([4, 3, 2, 1])

# Use the tuple of arrays to index and select specific elements
selected_elements = array_2d[row_indices, col_indices]

# Print the original array and the selected elements
print('Original 2D array:\n', array_2d)
print('Row indices:\n', row_indices)
print('Column indices:\n', col_indices)
print('Selected elements:\n', selected_elements)

Output:

Original 2D array:
 [[ 7 74 80 19  2]
 [63 29 42  4 36]
 [94 37 96 21 90]
 [28 81 62  7 66]
 [13  3 60 40 89]]
Row indices:
 [0 1 2 3]
Column indices:
 [4 3 2 1]
Selected elements:
 [ 2  4 96 81]

Explanation:

Import Libraries:

Imported numpy as 'np' for array creation and manipulation.

Create 2D NumPy Array:

Create a 2D NumPy array named array_2d with random integers ranging from 0 to 99 and a shape of (5, 5).

Define Row and Column Indices:

Defined row_indices and col_indices arrays to specify the rows and columns from which to select elements.

Tuple of Arrays Indexing:

Used a tuple of arrays (row_indices, col_indices) to index and select specific elements from array_2d.

Print Results:

Print the original 2D array, the row and column indices, and the selected elements to verify the indexing operation.

For more Practice: Solve these Related Problems:

Create a 2D array and use a tuple of index arrays to select elements at positions (0,1), (1,2), and (2,0).
Write a function that returns a diagonal subarray from a 2D array using a tuple of indices.
Implement a solution that uses a tuple of arrays to swap non-adjacent elements in a 2D array.
Use tuple indexing to extract a checkerboard pattern from a 2D array.

Go to:

Previous: Boolean Indexing on 3D NumPy arrays with conditions.
Next: Cross-Indexing a 2D NumPy array using np.ix_.

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