Hoping someone can help me with some graphics. Here is my data set. A B 1 5 1 5 1 6 2 7 3 7 4 7 5 8 6 9 6 10 7 11 Using this code, I split the data into two groups, each of size 5, and made a scatterplot. Bill<-read.table('something here') attach(Bill)Bill.s<-split(Bill, rep(1:2, each=5)) plot(A,B,col='black') $`1` A B1 1 52 1 53 1 64 2 75 3 7 $`2` A B 6 4 7 7 5 8 8 6 9 9 6 1010 7 11 For each group, I calculate the mean of B....For group 1, mean of B is 6. For group 2, mean of B is 9. On the scatterplot of A vs. B, for group 1, I want a horizontal line at the mean of 6. It should only cover group 1. For group 2, a horizontal line at the mean of 9. Again, should only cover the points in group 2. The endpoints of the different horizontal lines must connect. Can anybody give me any help? Thanks in advance. Bill _________________________________________________________________ sh_skydrive_062008 [[alternative HTML version deleted]]