How to add a border around a NumPy array?

Sometimes we need to add a border around a NumPy matrix. Numpy provides a function known as ‘numpy.pad()’ to construct the border. The below examples show how to construct a border of ‘0’ around the identity matrix.

Syntax :

numpy.pad(array, pad_width, mode='constant', **kwargs)  

Example 1: Construct a border of 0s around 2D identity matrix

Python3

# importing Numpy package
import numpy as np

# Creating a 2X2 Numpy matrix
array = np.ones((2, 2))

print("Original array")
print(array)

print("\n0 on the border and 1 inside the array")

# constructing border of 0 around 2D identity matrix
# using np.pad()
array = np.pad(array, pad_width=1, mode='constant',
               constant_values=0)

print(array)

Output:

In the above examples, we construct a border of 0s around the 2-D NumPy matrix.

Example 2: Construct a border of 0s around 3D identity matrix

Python3

# importing Numpy package
import numpy as np

# Creating a 3X3 Numpy matrix
array = np.ones((3, 3))

print("Original array")
print(array)

print("\n0 on the border and 1 inside the array")

# constructing border of 0 around 3D identity matrix
# using np.pad()
array = np.pad(array, pad_width=1, mode='constant',
               constant_values=0)

print(array)

Output:

In the above examples, we construct a border of 0s around the 3-D NumPy matrix.

Example 3: Construct a border of 0s around 4D identity matrix

Python3

# importing Numpy package
import numpy as np

# Creating a 4X4 Numpy matrix
array = np.ones((4, 4))

print("Original array")
print(array)

print("\n0 on the border and 1 inside the array")

# constructing border of 0 around 4D identity matrix
# using np.pad()
array = np.pad(array, pad_width=1, mode='constant',
               constant_values=0)

print(array)

Output:

In the above examples, we construct a border of 0s around the 4-D NumPy matrix.