1、概述

argsort()函数在模块numpy.core.fromnumeric中。

函数形式是：

help (numpy.argsort)

Help on function argsort in module numpy.core.fromnumeric:

argsort(a, axis=-1, kind='quicksort', order=None)

Returns the indices that would sort an array.

Perform an indirect sort along the given axis using the algorithm specified

by the `kind` keyword. It returns an array of indices of the same shape as

`a` that index data along the given axis in sorted order.

Parameters

----------

a : array_like

Array to sort.

axis : int or None, optional

Axis along which to sort. The default is -1 (the last axis). If None,

the flattened array is used.

kind : {'quicksort', 'mergesort', 'heapsort'}, optional

Sorting algorithm.

order : str or list of str, optional

When `a` is an array with fields defined, this argument specifies

which fields to compare first, second, etc. A single field can

be specified as a string, and not all fields need be specified,

but unspecified fields will still be used, in the order in which

they come up in the dtype, to break ties.

Returns

-------

index_array : ndarray, int

Array of indices that sort `a` along the specified axis.

If `a` is one-dimensional, ``a[index_array]`` yields a sorted `a`.

argsort()函数返回的是数组值从小到大的索引值。

排序后会产生一个新的数组，不改变原有的数组。

2、使用

一维数组

a = array([1,4,9,3,2,3,8])

b = a.argsort()

print(a)

print(b)

output:

[1 4 9 3 2 3 8]

[0 4 3 5 1 6 2]二维数组

x = array([[0, 3], [1, 2]])

print(x)

# [[0 3]

# [1 2]]

b = argsort(x) #默认按最后一维(列)排序

print(b)

# [[0 1]

# [0 1]]

c = argsort(x, axis=0) #按行排序

print(c)

# [[0 1]

# [1 0]]

d = argsort(x, axis=1) #按列排序

print(d)

# [[0 1]

# [0 1]]

其他使用示例：

x = array([1,3,2])

print(x)

# [1 3 2]

b = argsort(x) #按升序排列

print(b)

#[0 2 1]

c = argsort(-x) #按降序排列

print(c)

# [1 2 0]

d = x[argsort(x)] #排序后的数组

print(d)

# [1 2 3]

3、argsort()[num]使用

z = argsort(x)[num] 与 y = arfsort(x)  z = y[sum]结果相同

x = array([1,3,2])

y = argsort(x)

print(y[1])

# 2

z = argsort(x)[1]

print(z)

# 2

y = argsort(x)

print(y[-1])

# 1

z = argsort(x)[-1]

print(z)

# 1