How to Sort a NumPy Array by a Specific Column?

Sorting NumPy Arrays Based on Specific Columns

This query addresses the need to sort a NumPy array according to its designated nth column. To illustrate, let's work with an array 'a':

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

Our goal is to sort the rows of matrix 'a' based on its second column, resulting in:

array([[7, 0, 5],
       [9, 2, 3],
       [4, 5, 6]])

To achieve this, we can harness the ability to slice NumPy arrays based on indices and leverage the argsort function. The code below demonstrates the solution:

sorted_a = a[a[:, 1].argsort()]

Breaking down this code:

1. a[:, 1]: This selects the second column of 'a'.
2. .argsort(): This generates an array of indices representing the sorted order of the elements in the second column.
3. a[a[:, 1].argsort()]: This rearranges the rows of 'a' according to the sorted indices, leading to the desired result.

The above is the detailed content of How to Sort a NumPy Array by a Specific Column?. For more information, please follow other related articles on the PHP Chinese website!