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]]
>
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--
Eik Vettorazzi
Institut für Medizinische Biometrie und Epidemiologie
Universitätsklinikum Hamburg-Eppendorf
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