R: [R] column sorting a matrix with indices returned

[Vito Muggeo]

A possible solution is using apply + order:

> apply(x,2,order)
     [,1] [,2] [,3]
[1,]    3    2    3
[2,]    1    3    2
[3,]    2    1    1
> apply(x,2,function(x)x[order(x)])
     [,1] [,2] [,3]
[1,]    2    3    5
[2,]    3    4    7
[3,]    4    6    8
>

best,
vito


----- Original Message -----
From: Rajarshi Guha <rxg218 at psu.edu>
To: R <r-help at stat.math.ethz.ch>
Sent: Thursday, May 20, 2004 4:11 PM
Subject: [R] column sorting a matrix with indices returned


> Hi,
>   I'm trying to translate some Matlab code to R and I'm trying to
> implement the behavior of Matlab's sort() which when applied to a matrix
> will sort the columns returning the column  sorted matrix as well as a
> matrix of permuted indices.
>
> Doing:
>
> > x <- matrix(c(3,4,2,6,3,4,8,7,5), nr=3)
> > x
>      [,1] [,2] [,3]
> [1,]    3    6    8
> [2,]    4    3    7
> [3,]    2    4    5
>
> What I want after sorting x are two matrices:
>
> (the column sorted x)
> 2 3 5
> 3 4 7
> 4 6 8
>
> and (the index matrix)
> 3 2 3
> 1 3 2
> 2 1 1
>
> Doing,
> > sx <- apply(x, c(2), sort, index.return=T)
>
> results in sx being a series of lists. I know I could then go through
> the list and create a sorted matrix and an index matrix.
>
> But is there a neater way to do this?
>
> Thanks,
>
> -------------------------------------------------------------------
> Rajarshi Guha <rxg218 at psu.edu> <http://jijo.cjb.net>
> GPG Fingerprint: 0CCA 8EE2 2EEB 25E2 AB04 06F7 1BB9 E634 9B87 56EE
> -------------------------------------------------------------------
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