Re: [R] Second largest element from each matrix row

From: Dimitris Rizopoulos <d.rizopoulos_at_erasmusmc.nl>
Date: Tue, 26 Apr 2011 14:26:51 +0200

one way is the following:

a <- matrix(rnorm(9), 3 ,3)

aa <- a[order(row(a), -a)]
matrix(aa, nrow(a), byrow = TRUE)[, 2]

I hope it helps.

Best,
Dimitris

On 4/26/2011 2:01 PM, Lars Bishop wrote:
> Hi,
>
> I need to extract the second largest element from each row of a
> matrix. Below is my solution, but I think there should be a more efficient
> way to accomplish the same, or not?
>
>
> set.seed(1)
> a<- matrix(rnorm(9), 3 ,3)
> sec.large<- as.vector(apply(a, 1, order, decreasing=T)[2,])
> ans<- sapply(1:length(sec.large), function(i) a[i, sec.large[i]])
> ans
>
> Thanks in advance for your help,
> Lars.
>
> [[alternative HTML version deleted]]
>
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-- 
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
Web: http://www.erasmusmc.nl/biostatistiek/

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Received on Tue 26 Apr 2011 - 12:30:15 GMT

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