Set elements in 3D NumPy array using Boolean Indexing

Last update on December 21 2024 07:40:19 (UTC/GMT +8 hours)

Setting Values with Boolean Indexing:

Write a NumPy program that creates a 3D NumPy array and uses boolean indexing to set elements that meet a condition to a new value.

Sample Solution:

Python Code:

import numpy as np

# Create a 3D NumPy array of shape (4, 4, 4) with random integers
array_3d = np.random.randint(0, 100, size=(4, 4, 4))

# Define the condition to set elements less than 50 to -1
condition = array_3d < 50

# Use boolean indexing to set elements that meet the condition to -1
array_3d[condition] = -1

# Print the original array and the modified array
print('Original 3D array:\n', array_3d)
print('Condition (elements < 50):\n', condition)
print('Modified 3D array with elements < 50 set to -1:\n', array_3d)

Output:

Original 3D array:
 [[[-1 -1 -1 -1]
  [-1 -1 -1 70]
  [-1 69 85 60]
  [81 63 -1 -1]]

 [[-1 61 61 82]
  [81 59 -1 74]
  [-1 -1 77 67]
  [80 99 -1 -1]]

 [[-1 -1 -1 66]
  [-1 58 -1 -1]
  [53 -1 75 -1]
  [61 65 92 -1]]

 [[84 94 71 -1]
  [59 85 -1 -1]
  [52 77 54 95]
  [-1 -1 -1 74]]]
Condition (elements < 50):
 [[[ True  True  True  True]
  [ True  True  True False]
  [ True False False False]
  [False False  True  True]]

 [[ True False False False]
  [False False  True False]
  [ True  True False False]
  [False False  True  True]]

 [[ True  True  True False]
  [ True False  True  True]
  [False  True False  True]
  [False False False  True]]

 [[False False False  True]
  [False False  True  True]
  [False False False False]
  [ True  True  True False]]]
Modified 3D array with elements < 50 set to -1:
 [[[-1 -1 -1 -1]
  [-1 -1 -1 70]
  [-1 69 85 60]
  [81 63 -1 -1]]

 [[-1 61 61 82]
  [81 59 -1 74]
  [-1 -1 77 67]
  [80 99 -1 -1]]

 [[-1 -1 -1 66]
  [-1 58 -1 -1]
  [53 -1 75 -1]
  [61 65 92 -1]]

 [[84 94 71 -1]
  [59 85 -1 -1]
  [52 77 54 95]
  [-1 -1 -1 74]]]

Explanation:

Import Libraries:

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

Create 3D NumPy Array:

Create a 3D NumPy array named array_3d with random integers ranging from 0 to 99 and a shape of (4, 4, 4).

Define Condition:

Define a condition to select elements in the array that are less than 50 using boolean indexing.

Boolean Indexing to Set Values:

Applied boolean indexing to set elements in array_3d that meet the condition (elements less than 50) to -1.

Print Results:

Print the original 3D array, the boolean condition array, and the modified 3D array to verify the operation.

Python-Numpy Code Editor: