On Mon, 10 Dec 2007, Neil Stewart wrote: > I would like to make a new vector with values taken from two existing > vectors conditional upon a third. At present I am doing this with a for loop > but wonder if there is not a neater way, given some of the very neat things > R can do. > > a<-rep(c("A","B"),50) > b<-rep(1,100) > c<-rep(2,100) > > a is thus "A" "B" "A" "B" "A" "B"... > b is thus 1 1 1 1 1 1 ... > c is thus 2 2 2 2 2 2 ... > > I want d[i] to be b[i] if a[i]=="A" and c[i] if a[i]=="B". I'm current using > a for loop: > > d<-rep(0,100) # initialise d > for(i in 1:length(a)) {if(a[i]=="A") d[i]<-b[i] else d[i]<-c[i]} > > d is thus 1 2 1 2 1 2 1 2 1 ... > > Is it possible to do something simpler, say along the lines of the c-style > ?: conditional statement, or at least avoiding the for loop. > > d <- a=="A"?b:c # doesn't work, but you get the idea
d <- ifelse(a == "A", b, c) is what you want! Z > Thanks in advance, > Neil > > ______________________________________________ > 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. > > ______________________________________________ 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.