HI, May be this helps: library(Ckmeans.1d.dp) ?set.seed(24) ?RanNum1<-runif(20,9,12) Ck1<-Ckmeans.1d.dp(RanNum1,4) ?plot(RanNum1,col=Ck1$cluster) ?abline(h=Ck1$centers,col=1:4,pch=8,cex=2) ?Ck1$cluster # [1] 2 2 3 3 3 4 2 4 4 2 3 2 3 3 2 4 2 1 3 1 which(Ck1$cluster==2,arr.ind=T) #[1]? 1? 2? 7 10 12 15 17 # res<-lapply(unique(Ck1$cluster),function(x) which(Ck1$cluster==x,arr.ind=T)) ?names(res)<- unique(Ck1$cluster) ?res #$`2` #[1]? 1? 2? 7 10 12 15 17 # #$`3` #[1]? 3? 4? 5 11 13 14 19 # #$`4` #[1]? 6? 8? 9 16 # #$`1` #[1] 18 20 A.K. Hello guys, sorry to bother you guys again but was wondering if I'm doing this correctly. I seem to have run into trouble. I've done the first two parts But I can't seem to understand how to do the last part with the which() function. This is what I came up with Am I on the right track? Or am I using this which() function incorrectly???