Here is a simple example of a simple question: dt<-data.table(a=rep(1:5,1:5),b=1,c=rep(1:3,5)) dt dt[,seq_along(b),by=a] # expected behavior (note: dt is already in order of a) setkey(dt,c) # to sort by c dt dt[,seq_along(b),by=a] # expected behavior? Appears to be in order of unique(dt$a)
Thanks, Joe Voelkel
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