Python中的 numpy.argsort()

numpy.argsort()函数用于使用 kind 关键字指定的算法沿给定轴执行间接排序。它返回一个与 arr 形状相同的索引数组，用于对数组进行排序。

Syntax : numpy.argsort(arr, axis=-1, kind=’quicksort’, order=None)

Parameters :
arr : [array_like] Input array.
axis : [int or None] Axis along which to sort. If None, the array is flattened before sorting. The default is -1, which sorts along the last axis.
kind : [‘quicksort’, ‘mergesort’, ‘heapsort’]Selection algorithm. Default is ‘quicksort’.
order : [str or list of str] When arr is an array with fields defined, this argument specifies which fields to compare first, second, etc.

Return : [index_array, ndarray] Array of indices that sort arr along the specified axis.If arr is one-dimensional then arr[index_array] returns a sorted arr.

代码#1：

# Python program explaining
# argpartition() function
   
import numpy as geek
  
# input array
in_arr = geek.array([ 2, 0,  1, 5, 4, 1, 9])
print ("Input unsorted array : ", in_arr) 
  
out_arr = geek.argsort(in_arr)
print ("Output sorted array indices : ", out_arr)
print("Output sorted array : ", in_arr[out_arr])

输出：

Input unsorted array :  [2 0 1 5 4 1 9]
Output sorted array indices :  [1 2 5 0 4 3 6]
Output sorted array :  [0 1 1 2 4 5 9]

代码#2：

# Python program explaining
# argpartition() function
  
import numpy as geek
  
# input 2d array
in_arr = geek.array([[ 2, 0, 1], [ 5, 4, 3]])
print ("Input array : ", in_arr) 
  
# output sorted array indices
out_arr1 = geek.argsort(in_arr, kind ='mergesort', axis = 0)
print ("Output sorteded array indices along axis 0: ", out_arr1)
out_arr2 = geek.argsort(in_arr, kind ='heapsort', axis = 1)
print ("Output sorteded array indices along axis 1: ", out_arr2)

输出：

Input array :  [[2 0 1]
 [5 4 3]]
Output sorteded array indices along axis 0:  [[0 0 0]
 [1 1 1]]
Output sorteded array indices along axis 1:  [[1 2 0]
 [2 1 0]]