[R] Still trying to avoid loops

[Rui Barradas]

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(rep('a',2),rep('b',1),rep('c',3)),levels=c('b','a','c')),
> 		D=c(5,1,3,2,3,4))
>
> 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
>
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