Quickly generate the cartesian product of a matrix

Question

Let\'s say I have a matrix x which contains 10 rows and 2 columns. I want to generate a new matrix M that contains each unique pair of rows from

Answer 1

Using Dirk's answer:

idx <- expand.grid(1:nrow(x), 1:nrow(x))
idx<-idx[idx[,1] >= idx[,2],]
N <- cbind(x[idx[,2],], x[idx[,1],])

> all(M == N)
[1] TRUE

Thanks everyone!