Yes, you remind me of this!
Thanks!


2011/8/16 Eik Vettorazzi <E.Vettorazzi@uke.uni-hamburg.de>

> Hi Lao,
> you tried to reinvent the wheel. Have a look at ?tapply
>
> tapply(sleep$extra,sleep$group,mean)
>
> Cheers
>
> Am 16.08.2011 09:41, schrieb Lao Meng:
> > Hi all:
> > My data:data(sleep)
> >
> > If I wanna calculate each group's extra,what I can do is:
> > #method1
> > attach(sleep)
> > mean(extra[group==1])
> > mean(extra[group==1])
> >
> >
> > #method2
> > result<-matrix(,0,2)
> > g<-split(sleep,sleep$group)
> > for(i in 1:length(g))
> > {
> > result<-rbind(result,data.frame(unique(g[[i]]$group),mean(g[[i]]$extra)))
> > }
> > colnames(result)<-c("name","mean")
> >
> > But the above 2 method is a little bit tedious.Is there a "short cut"
> manner
> > to get the same result?
> >
> > Thanks a lot!
> >
> > My best
> >
> >       [[alternative HTML version deleted]]
> >
> > ______________________________________________
> > 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.
>
> --
> Eik Vettorazzi
> Institut für Medizinische Biometrie und Epidemiologie
> Universitätsklinikum Hamburg-Eppendorf
>
> Martinistr. 52
> 20246 Hamburg
>
> T ++49/40/7410-58243
> F ++49/40/7410-57790
>

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