How to use NumPy to sort by column in an array?

This recipe explains how to use NumPy to sort by column in an array in Python.

Efficiently organizing and manipulating data is a fundamental aspect of data science and numerical computing. NumPy, a Python ibrary, offers a variety of tools to work with arrays and matrices. In this guide, we will delve into the world of sorting NumPy arrays by columns, a crucial skill for various data analysis and manipulation tasks. Whether you need to sort by the first column, second column, or any other column, NumPy provides a straightforward method for achieving this. Let's explore how to use NumPy to sort by a specific column efficiently.

Learn how to build Regression (Linear,Ridge,Lasso) Models in NumPy Python 

How to sort NumPy Array by column in Python?

Learn how to sort a numpy array by a column with these easy-to-follow steps

Step 1: Importing the NumPy library

Begin by importing the NumPy library into your Python environment. NumPy is a versatile library that is instrumental in data manipulation and enables a range of mathematical operations.

import numpy as np

This import is the starting point for utilizing NumPy's array sorting functions effectively.

Step 2: Define a Random NumPy Array

Before we teach your how to sort an array by column using numpy, you need to create a random NumPy array with multiple rows and columns. For this example, we've defined a sample 2D array to demonstrate the sorting process.

a = np.array([[9, 2, 3],[4, 5, 6],[7, 0, 5]])

This 'a' array serves as our data to be sorted by one of its columns.

Step 3: Use NumPy to sort 2D array by Second column

To sort the NumPy array by a particular column, use NumPy's argsort() function. In this example, we're sorting the array by the second column (index 1). The sorted array will be stored in 'a'.

a = a[a[:,1].argsort()] 

print(a)

This code efficiently sorts 'a' by its second column. You can adapt this code to sort by any other column of interest. For example, if you want to learn how to sort a NumPy 2D array by first  column, use ‘0’ index instead of ‘1’ index.

Scroll down to the ipython file below to visualize the output.

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The ability to sort NumPy arrays by columns is a valuable skill that finds application in various data science problems. NumPy's straightforward sorting methods streamline the process and enhance your data manipulation capabilities. Whether you are working with large datasets, conducting statistical analyses, or organizing information for further research, NumPy's sorting functionality can significantly improve your workflow.

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