From: David Winsemius <dwinsemius_at_comcast.net>

Date: Tue, 26 Apr 2011 08:36:11 -0400

Date: Tue, 26 Apr 2011 08:36:11 -0400

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 ______________________________________________ R-help_at_r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.Received on Tue 26 Apr 2011 - 12:38:06 GMT

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