Try this: f$E <- diag(as.matrix(f[f$D]))
On Wed, Jun 9, 2010 at 11:03 AM, Malcolm Fairbrother < m.fairbrot...@bristol.ac.uk> wrote: > Dear all, > > I have a data frame f, with four variables: > > f <- data.frame(A=c(0,0,1,1), B=c(0,1,0,1), C=c(1,1,0,1), D=c(3,1,2,3)) > f > A B C D > 1 0 0 1 3 > 2 0 1 1 1 > 3 1 0 0 2 > 4 1 1 1 3 > > I want to create a new variable (f$E), such that each of its elements is > drawn from either f$A, f$B, or f$C, according to the value (for each row) of > f$D (values of which range from 1 to 3). > > In the first row, D is 3, so I want the value from the third variable (C), > which for the first row is 1. In the second row, D is 1, so I want the value > from the first variable (A), which for the second row is 0. And so forth, > such that in the end my new data frame looks like: > > A B C D E > 1 0 0 1 3 1 > 2 0 1 1 1 0 > 3 1 0 0 2 0 > 4 1 1 1 3 1 > > My question is: How do I do this for a much larger dataset, where my "index > variable" (f$D in this example) actually indexes a much larger number of > variables (not just three)? > > I know that in principle I could do this with a long series of nested > ifelse statements (as below), but I assume there is some less cumbersome > option, and I'd like to know what it is. Any help would be much appreciated. > Apologies if I'm missing something obvious. > > f$E <- ifelse(f$D==3, f$C, ifelse(f$D==2, f$B, f$A)) > > Thanks, > Malcolm > > ______________________________________________ > R-help@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. > -- Henrique Dallazuanna Curitiba-Paraná-Brasil 25° 25' 40" S 49° 16' 22" O [[alternative HTML version deleted]]
______________________________________________ R-help@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.
