[R] reordering of matrix rows to maximize the sum of the diagonal
Jonathan
jonsleepy at gmail.com
Fri Apr 23 22:49:26 CEST 2010
Hi Dimitris,
This code is very helpful, although I note that the columns are not
preserved, ie if
> M <- matrix(sample(13, 9, TRUE), 3, 3)
produces:
> M
[,1] [,2] [,3]
[1,] 13 9 2
[2,] 10 1 12
[3,] 11 6 7
then
> n <- ncol(M)
> ind <- apply(M, 2, which.max)
> maxs <- M[cbind(ind, 1:n)]
> diags <- diag(M)
> diag(M) <- M[cbind(ind, 1:n)]
> M[cbind(ind, 1:n)] <- diags
produces
> M
[,1] [,2] [,3]
[1,] 13 1 2
[2,] 10 9 7
[3,] 11 6 12
The diagonal is maximized, but the rows are no longer the same. For
example, row 1 of the original matrix was 13 9 2, and in the second
matrix, it is 13 1 2.
I'm looking to conserve the rows, but only reorder them vertically.
Thanks,
Jonathan
On Fri, Apr 23, 2010 at 4:32 PM, Dimitris Rizopoulos
<d.rizopoulos at erasmusmc.nl> wrote:
> one way is:
>
> M <- matrix(sample(13, 9, TRUE), 3, 3)
>
> n <- ncol(M)
> ind <- apply(M, 2, which.max)
> maxs <- M[cbind(ind, 1:n)]
> diags <- diag(M)
> diag(M) <- M[cbind(ind, 1:n)]
> M[cbind(ind, 1:n)] <- diags
> M
>
>
> I hope it helps.
>
> Best,
> Dimitris
>
>
> On 4/23/2010 10:10 PM, Jonathan wrote:
>>
>> Hi r-help community,
>> This question isn't so much a syntax/coding one, but here goes:
>>
>> Let's say I have matrix of arbitrary dimensions and I'd like to
>> reorder the rows in such a way that I could maximize the sum of the
>> entries along the diagonal.
>>
>> For example, for this 3x3 matrix:
>>
>>
>> [,1] [,2] [,3]
>> [1,] 3 4 13
>> [2,] 9 1 2
>> [3,] 2 11 1
>>
>> rearranging the rows to maximize the sum along the diagonal would
>> produce this matrix:
>>
>> [,1] [,2] [,3]
>> [1,] 9 1 2
>> [2,] 2 11 1
>> [3,] 3 4 13
>>
>>
>> I've been experimenting with some scripts of my own, but I figured I'd
>> ask if one of you R-ninjas might know of an existing function (or
>> algorithm I could look up and then code) that can do this somewhat
>> efficiently (or even just correctly!).
>>
>> Best,
>> Jonathan
>>
>> ______________________________________________
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>> PLEASE do read the posting guide
>> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
>
> --
> Dimitris Rizopoulos
> Assistant Professor
> Department of Biostatistics
> Erasmus University Medical Center
>
> Address: PO Box 2040, 3000 CA Rotterdam, the Netherlands
> Tel: +31/(0)10/7043478
> Fax: +31/(0)10/7043014
>
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