[R] reordering of matrix rows to maximize the sum of the diagonal

[Dimitris Rizopoulos]

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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-- 
Dimitris Rizopoulos
Assistant Professor
Department of Biostatistics
Erasmus University Medical Center

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