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Hi again, Awfully sorry John, I should have been sleeping and did not see your full post.... here is a way, unless I miss the point again : fake<-as.data.frame(cbind(seq(1,10,by=1),c(rep(1,4),rep(0,4),rep(2,2)))) # from my previous post # one moree column this time ! fake3<-cbind(fake,fake$V2) index<-c(2,3) fake3[,index][fake3[,index]==0]<-NA not nice, but seems to do the job. Hope this helps... this time :-) Olivier -- Olivier ETERRADOSSI Ma?tre-Assistant CMGD / Equipe "Propri?t?s Psycho-Sensorielles des Mat?riaux" Ecole des Mines d'Al?s H?...