Learning NumPy: Adding Columns to Arrays – A Practical Guide

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.

Additional Resources

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