Mike wrote: >Hi, there, > >Suppose I have two vector say x=c(1 2 3 4 5) and y=(2 >3 6 7). Then I want to combine these two vector >together and get z=c(1 2 3 4 5 6 7) with 2 and 3 only >appear once. > union(x,y) R provides several set operators. See ?union. Christophe Pallier