[R] Still trying to avoid loops

[Bert Gunter]

tapply() (of which by() is essentially a wrapper) **is** a (disguised)
loop (at the R level, of course).

Cheers,
Bert



Bert Gunter
Genentech Nonclinical Biostatistics
(650) 467-7374

"Data is not information. Information is not knowledge. And knowledge
is certainly not wisdom."
Clifford Stoll




On Wed, Feb 4, 2015 at 11:49 AM, Rui Barradas <ruipbarradas at sapo.pt> 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(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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>>
>
> ______________________________________________
> 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.