Extracting first n columns of a NumPy matrix

Learn how to extract first n columns of a NumPy matrix in Python?
By Pranit Sharma Last updated : December 28, 2023

NumPy is an abbreviated form of Numerical Python. It is used for different types of scientific operations in python. Numpy is a vast library in python which is used for almost every kind of scientific or mathematical operation. It is itself an array which is a collection of various methods and functions for processing the arrays.

Slicing is the technique that will help us to find the first n columns of this numpy array.

NumPy Matrix - Extracting first n columns

Suppose that we are given a multi-dimensional numpy array with certain rows and columns and we just need to extract the first n columns of this numpy array.

Suppose that we have an array a which contains 5 columns and we need to extract its first 3 columns, we will use the following slicing code to extract the first 3 columns: a[: , : , 3]

Let us understand with the help of an example,

Python code to extract first n columns of a NumPy matrix

# Import numpy
import numpy as np

# Creating a numpy array
arr =  np.array([[1, 2, 3, 4, 5],
        [4, 5, 6, 7, 8],
        [7, 8, 9, 10, 11]])

# Display original array
print("Original array:\n",arr,"\n")

# Slicing the array and extracting
# first 3 columns
res = arr[:,:3]

# Display Result
print("Result:\n",res,"\n")