How to sort a two-dimensional array according to a row or column in Python

This article mainly introduces Python's method of sorting two-dimensional arrays according to a certain row or column. It analyzes the common operating techniques of Python using the lexsort method of the numpy module to sort two-dimensional arrays based on specific examples. Friends who need it You can refer to the following

The example of this article describes how Python implements the method of sorting a two-dimensional array according to a certain row or column. Share it with everyone for your reference, the details are as follows:

lexsort supports sorting arrays in the order of specified rows or columns; it is indirect sorting, lexsort does not modify the original array and returns the index.

(Corresponding to lexsort one-dimensional array is argsort a.argsort()You can use it this way; argsort does not modify the original array and returns the index)

The default is to press the last The elements in a row are sorted from small to large, and the index position of the last row of elements after sorting is returned.

Suppose array a, the returned index ind, ind returns a one-dimensional array

For a one-dimensional array, a[ind] is the sorted array.

For two-dimensional arrays, detailed examples will be given below.

import numpy as np
>>> a
array([[ 2, 7, 4, 2],
    [35, 9, 1, 5],
    [22, 12, 3, 2]])

Sort by last column order

>>> a[np.lexsort(a.T)]
array([[22, 12, 3, 2],
    [ 2, 7, 4, 2],
    [35, 9, 1, 5]])

Sort by last column in reverse order

>>>a[np.lexsort(-a.T)]
array([[35, 9, 1, 5],
    [ 2, 7, 4, 2],
    [22, 12, 3, 2]])

By first column Sort in order

>>> a[np.lexsort(a[:,::-1].T)]
array([[ 2, 7, 4, 2],
    [22, 12, 3, 2],
    [35, 9, 1, 5]])

Sort in order of the last row

>>> a.T[np.lexsort(a)].T
array([[ 2, 4, 7, 2],
    [ 5, 1, 9, 35],
    [ 2, 3, 12, 22]])

Sort in order of the first row

>>> a.T[np.lexsort(a[::-1,:])].T
array([[ 2, 2, 4, 7],
    [ 5, 35, 1, 9],
    [ 2, 22, 3, 12]])

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