ndarry大小排序返回下标 --- argsort函数用法

末蓝、 2021-12-10 03:43 334阅读 0赞

在Python中使用help帮助

>>> import numpy  
>>> 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.

从中可以看出argsort函数返回的是数组值从小到大的索引值

Examples  
\--------  
One dimensional array:一维数组  
  
>>> x = np.array(\[3, 1, 2\])  
>>> np.argsort(x)  
array(\[1, 2, 0\])  
  
Two-dimensional array:二维数组  
  
>>> x = np.array(\[\[0, 3\], \[2, 2\]\])  
>>> x  
array(\[\[0, 3\],  
\[2, 2\]\])  
  
>>> np.argsort(x, axis=0) \#按列排序  
array(\[\[0, 1\],  
\[1, 0\]\])  
  
>>> np.argsort(x, axis=1) \#按行排序  
array(\[\[0, 1\],  
\[0, 1\]\])

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例1：

>>> x = np.array(\[3, 1, 2\])  
>>> np.argsort(x) \#按升序排列  
array(\[1, 2, 0\])  
>>> np.argsort(-x) \#按降序排列  
array(\[0, 2, 1\])

>>> x\[np.argsort(x)\] \#通过索引值排序后的数组  
array(\[1, 2, 3\])  
>>> x\[np.argsort(-x)\]  
array(\[3, 2, 1\])

另一种方式实现按降序排序：

>>> a = x\[np.argsort(x)\]  
>>> a  
array(\[1, 2, 3\])  
>>> a\[::-1\]  
array(\[3, 2, 1\])

另外说到排序，还有两个常用的函数sort和sorted，详细内容请看：[http://maoersong.blog.163.com/blog/static/171557351201424105925681/?newFollowBlog][http_maoersong.blog.163.com_blog_static_171557351201424105925681_newFollowBlog]

[http_maoersong.blog.163.com_blog_static_171557351201424105925681_newFollowBlog]: http://maoersong.blog.163.com/blog/static/171557351201424105925681/?newFollowBlog