M <- matrix(c(rep(4:6,2),rep(1:3,2),seq(0.1,0.6,0.1)),6,3)
> colnames(M)=c("s1","s2","p")
> unique(M[,1:2])
     s1 s2
[1,]  4  1
[2,]  5  2
[3,]  6  3

s1 s2 p1  p2
[1,]  4  1  0.1 0.4
[2,]  5  2  0.2 0.5
[3,]  6  3  0.3 0.6