NumPy: Add a border around an existing array

Last update on August 29 2025 12:46:18 (UTC/GMT +8 hours)

Add Border to Array (0s)

Write a NumPy program to add a border (filled with 0's) around an existing array.

Python NumPy: Add a border around an existing array

Sample Solution:

Python Code:

# Importing the NumPy library with an alias 'np'
import numpy as np

# Creating a 3x3 NumPy array filled with ones
x = np.ones((3, 3))

# Printing the original array 'x'
print("Original array:")
print(x)

# Modifying the array 'x' to set 0s on the border and 1s inside the array using the np.pad function
print("0 on the border and 1 inside in the array")
x = np.pad(x, pad_width=1, mode='constant', constant_values=0)

# Printing the modified array 'x' with 0s on the border and 1s inside
print(x)

Sample Output:

Original array:                                                         
[[ 1.  1.  1.]                                                          
 [ 1.  1.  1.]                                                          
 [ 1.  1.  1.]]                                                         
1 on the border and 0 inside in the array                               
[[ 0.  0.  0.  0.  0.]                                                  
 [ 0.  1.  1.  1.  0.]                                                  
 [ 0.  1.  1.  1.  0.]                                                  
 [ 0.  1.  1.  1.  0.]                                                  
 [ 0.  0.  0.  0.  0.]]

Explanation:

In the above code –

x = np.ones((3,3)): Creates a 3x3 NumPy array filled with ones.

x = np.pad(x, pad_width=1, mode='constant', constant_values=0): The np.pad function is used to pad the input array x with a border of specified width and values. In this case, pad_width=1 adds a border of width 1 around the array. The mode='constant' specifies that the padding should be done with constant values, and constant_values=0 indicates that the constant value for padding should be 0.

For more Practice: Solve these Related Problems:

Pad a given 2D array with a border of zeros using np.pad and verify the new dimensions.
Create a function that adds a customizable border around any input array.
Append a zero border to an array and then check that the original data remains unchanged.
Compare different padding modes to add a border of zeros around a matrix and analyze the outcomes.

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