You can use one of the following methods to add a column to a NumPy array:

Method 1: Append Column to End of Array

np.append(my_array, [[value1], [value2], [value3], ...], axis=1)

Method 2: Insert Column in Specific Position of Array

np.insert(my_array, 3, [value1, value2, value3, ...], axis=1) 

The following examples show how to use each method in practice.

Example 1: Append Column to End of NumPy Array

Suppose we have the following NumPy array:

import numpy as np

#create NumPy array
my_array = np.array([[1, 2, 3, 4], [5, 6, 7, 8]])

#view NumPy array
my_array

array([[1, 2, 3, 4],
       [5, 6, 7, 8]])

We can use the following syntax to add a column to the end of the NumPy array:

#append column to end of NumPy array
new_array = np.append(my_array, [[10], [13]], axis=1)

#view updated array
new_array

array([[ 1,  2,  3,  4, 10],
       [ 5,  6,  7,  8, 13]])

Example 2: Insert Column in Specific Position of NumPy Array

Suppose we have the following NumPy array:

import numpy as np

#create NumPy array
my_array = np.array([[1, 2, 3], [4, 5, 6], [7, 8, 9]])

#view NumPy array
my_array

array([[1, 2, 3],
       [4, 5, 6],
       [7, 8, 9]])

We can use the following syntax to insert a new column before the column in index position 2 of the NumPy array:

#insert new column before column in index position 2
new_array = np.insert(my_array, 2, [10, 13, 19], axis=1)

#view updated array
new_array

array([[ 1,  2, 10,  3],
       [ 4,  5, 13,  6],
       [ 7,  8, 19,  9]])

Notice that the new column of values has been inserted before the column in index position 2.

The following tutorials explain how to perform other common operations in NumPy: