[R] Second largest element from each matrix row

[Dimitris Rizopoulos]

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

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