topic Re: Sort a matrix in Discussions

Sort a matrix

uday_guntupalli — Wed, 12 Dec 2018 11:44:13 GMT

All,
Is there a way to achieve functionality similar to what is shown below :

A = [10 -12 4 8; 6 -9 8 0; 2 3 11 -2; 1 1 9 3]

Upon sorting, how can i retain the original positions of the elements ?

For e.g. if i wanted to sort each column of the matrix, I can only think of doing the following:

for(i = 1, i <= N cols(A), i ++,
          t = A[0,i]; 
          t1 = sort descending(t); 
    );

Now, how can I determine the original position of the elements and retain them ?
https://www.mathworks.com/help/matlab/ref/sort.html - In Matlab, there is a second argument to the sort function which returns the index

Similarly in R, you can retain the index. Wondering what is the best way to do that in JMP ?

Re: Sort a matrix

txnelson — Wed, 12 Dec 2018 13:20:20 GMT

Take a look at "Ranking and Sorting" in the "Data Structures, Matrices" section of the Scripting Guide

Re: Sort a matrix

uday_guntupalli — Wed, 12 Dec 2018 14:16:37 GMT

@txnelson,
I believe you are referring to the content that is also covered here - https://www.jmp.com/support/help/14/ranking-and-sorting.shtml . However, this does not expand on capturing the indices that I am looking for while performing the sort. Hopefully, I am not missing something.

Re: Sort a matrix

Mark_Bailey — Wed, 12 Dec 2018 14:44:48 GMT

Um, it is the ranking bit...

Re: Sort a matrix

uday_guntupalli — Wed, 12 Dec 2018 15:10:46 GMT

@Mark_Bailey & @txnelson,
I understand that it looks obvious to you that Rank() does what I want, however , here is an example of why I am asking for:

In Matlab, here is what happen when you try to sort a matrix. Apologies for pulling this example from a different platform, I tried to avoid doing that but I can't think of a better way to explain what I am after. So if you look at the values of "I", it retains the indices

Now, if I wanted to do the exact samething in JMP , is this the way you are recommending me to take, it yes, it doesn't get me the same result. Also, I would appreciate not having to use a loop for something like this

A = [10 -12 4 8; 6 -9 8 0; 2 3 11 -2; 1 1 9 3];

for(i = 1 , i <= N Cols(A), i++,
		t = A[0,i]; 
		t1 = Sort Descending(t); 
		ranks = Rank(t); 
   );

Re: Sort a matrix

Mark_Bailey — Wed, 12 Dec 2018 16:17:14 GMT

This adaption should work:

A = [10 -12 4 8; 6 -9 8 0; 2 3 11 -2; 1 1 9 3];

sort matrix = Function( { m }, { t, b=[], i=[] },
 For( j = 1, j <= N Cols( m ), j++,
 t = A[0,j];
 b ||= Sort Descending( t );
 i ||= Matrix( Reverse( As List( Rank Index( t ) ) ) );
 );
 Eval List( { b, i } );
);

{ B, I } = sort matrix( A );

Show( A, B, I );

Re: Sort a matrix

uday_guntupalli — Wed, 12 Dec 2018 18:20:42 GMT

@Mark_Bailey,
Thank you. I will submit a request to the wish list to provide a canned function for this. I hope in the future, JMP will come up with a way to not have to loop through the matrix. I would love to see the apply() function family from R introduced into JMP.