Am 22.07.2010 11:18, schrieb Christian Schoder:
> I use the plm package and work with firm-level data in a panel. I would
> like to eliminate all firms that do not fulfill the requirement of
> having an observation in every variable used for at least x consecutive
> years.
There are probably more ellegant solutions but you could do something like:
test<-data.frame(year=c(2001,2001,2002,2001,2002,2003),id=c(1,2,2,3,3,3),x=runif(6))
test1<-aggregate(test,by=list(id=test$id),FUN=c("length","mean"))
test2<-merge(test,test1[,c("id","x")],by.x="id",by.y="id")
names(test2)<-c(names(test),"count")
testsub<-subset(test2,count>2)
testsub
hth
Stefan
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