[R] [basic ?] Merging result of by processing with a data fra me

[Liaw, Andy]

> From: Jean-Louis Abitbol
> 
> Dear All,
> 
> I would like to merge a data frame such as:
> 
> > basetab
>    subject dose  cmax
> 1     1031   50  21.8
> ....
> 
> with the result of a by processing such as:
> 
> > tmax<-by(pkga,subject,f.tmax)
> > tmax
> subject: 1031
> [1] 6
> --------------------------------------------------
> 
> f.tmax being a function written by H. Nguyen (in applied statistics in
> the pharmaceutical industry). pkga is a data frame with subject conc
> time variates.
> 
> The aim is to have a single data frame with subject dose cmax tmax etc
> (AUCs) ... so that I can do summary stats and plots by dose.

I would use tapply() instead of by().  Something like the following might
work (assuming `subject' is factor, as I believe it should be):

tmax <- tapply(pkga, subject, f.tmax)
tmax <- data.frame(subject=factor(names(tmax), tmax=tmax)

Then use merge() to merge basetab with tmax, or if all subjects are present
and in the same order, just cbind() them.

Andy
 
> I have tried unlist without success.
> 
> Thanks for any help.
> 
> Kind regards, Jean-Louis
> 
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