N<-200
c1<-cbind(rnorm(N, mean=0),rnorm(N, mean=5), rep(1,N))
c2<-cbind(rnorm(N, mean=0),rnorm(N, mean=-5), rep(2,N))
cx<-rbind(c1,c2)
plot(cx,col=cx[,3], xlim=c(-10,10), ylim=c(-10,10))