R help - Jul 2006 - R: the first and last case

could it be

 dat[unlist(tapply(1:nrow(dat), ind, range)),]
?

stefano



   >-----Messaggio originale-----
   >Da: r-help-bounces at stat.math.ethz.ch
   >[mailto:r-help-bounces at stat.math.ethz.ch]Per conto di 
   >Mauricio Cardeal
   >Inviato: 26 July, 2006 14:22
   >A: r-help at stat.math.ethz.ch
   >Oggetto: [R] the first and last case
   >
   >
   >Hi all
   >
   >Sometime ago I asked for a solution about how to aggregate 
   >data and the 
   >help was wonderful. Now, I?d like to know how to extract for each 
   >individual case below the first and the last observation to 
   >obtain this:
   >
   >ind  y
   >1    8
   >1    9
   >2    7
   >2   11
   >3    9
   >3   10
   >4   8
   >4   5
   >
   ># Below the example:
   >
   >ind <- c(1,1,1,2,2,3,3,3,4,4,4,4)
   >y <- c(8,10,9,7,11,9,9,10,8,7,6,5)
   >dat <- as.data.frame(cbind(ind,y))
   >dat
   >attach(dat)
   >mean.ind <- aggregate(dat$y, by=list(dat$ind), mean)
   >mean.ind
   >
   >Thanks
   >Mauricio
   >
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