[R] Still trying to avoid loops

[Tom Wright]

Thanks, I was not aware of order().
I did deliberately mess up the order of S. The following example breaks
your solution
dat_2<-data.frame(S=factor(c('a','c','a','b','c','c')),
		  D=c(5,3,1,3,2,4))

which should give the answer c(2,2,1,1,2,3)

Your solution does indicate that sorting the data correctly before
starting might solve the problem.


On Wed, 2015-02-04 at 19:49 +0000, Rui Barradas wrote:
> Hello,
> 
> Aren't the levels of your example wrong? If the levels are 
> levels=c('a','b','c'), not c('b', 'a', 'c'), then the following will do 
> the job.
> 
> unname(unlist(tapply(dat$D, dat$S, order)))
> 
> 
> Hope this helps,
> 
> Rui Barradas
> 
> Em 04-02-2015 19:34, Tom Wright escreveu:
> > Given a dataframe:
> > dat<-data.frame(S=factor(c('a','b','a','c','c','c',levels=c('b','a','c')),
> > 		D=c(1,5,3,2,3,4))
> >
> > where S is a subject identifier and D a visit (actually a date in my
> > real dataset). I would like to generate another column giving the visit
> > number
> >
> > R=c(2,1,1,1,2,3)
> >
> > My current solution uses nested loops and is slow and ugly. I've looked
> > at by() but can't see how to keep the order of R correct.
> >
> > Thanks,
> > Tom
> >
> > ______________________________________________
> > R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> > 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.
> >