numpy基础——numpy.argsort

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本文详细介绍了 numpy 中的 argsort 函数，该函数能够返回数组排序后的索引，并且可以根据需求选择不同的排序算法。适用于一维及多维数组的排序需求。

numpy.argsort

numpy.argsort(a, axis=-1, kind=’quicksort’, order=None)

Returns the indices that would sort an array.
返回排序数组的索引。

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.
使用kind关键字指定的算法沿给定轴进行间接排序。它按照排序的顺序返回与给定轴的索引数据相同形状的索引数组。

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.

Examples

One dimensional array:

返回的结果为输入数组元素从小到大的索引

>>> x = np.array([3, 1, 2])
>>> np.argsort(x)
array([1, 2, 0])

Two-dimensional array:

>>> x = np.array([[0, 3], [2, 2]])

>>> x
array([[0, 3],
       [2, 2]])

>>> np.argsort(x, axis=0)
array([[0, 1],
       [1, 0]])

>>> np.argsort(x, axis=1)
array([[0, 1],
       [0, 1]])