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.
