[Numpy-discussion] array sort questions

Tim Hochberg tim.hochberg at ieee.org
Wed Sep 17 13:19:21 EDT 2003

CL WU wrote:

> Hi, group,
>          I am new to numpy. I have 2 questions for array sort.
> 1. How to sort an array by its one column or one row?
>    I know python build-in sort() can do it for list by passing own cmp 
> function. but array function sort() will sort each column or row 
> seperately,as I know. I don't want to convert array to list to sort 
> and then convert back to array.

I think you want argsort plus take. For example, the following sorts on 
the second column of a:

     a = array([[4,5,6], [1,2,3], [7,8,9]])
     arg = argsort(a[:,1])
     take(a, arg, 0)

> 2. How to get the rank of a rank-0 array? The first "rank" means the 
> order of each element after sorting, instead of the "dimension" 
> meaning in numpy.     Just like "rank()" function in splus.

If  I understand you correctly, you want argsort as mentioned above.



> Thank you
> Chunlei
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