On Apr 26, 2011, at 8:01 AM, 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
There are probably many but this one is reasonably compact, one-step,
and readable:
> ans2 <- apply(a, 1, function(i) sort(i)[ dim(a)[2]-1])
> ans2
Refreshing my mail client proves I was right about many solutions, but
this is the first (so far) to use the dim attribute.
--
David Winsemius, MD
West Hartford, CT
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