Are you aware of the set.seed()
command?
R> set.seed(42); runif(3)
[1] 0.914806 0.937075 0.286140
R> set.seed(42); runif(3) # same seed, same numbers
[1] 0.914806 0.937075 0.286140
R> set.seed(12345); runif(3) # different seed, different numbers
[1] 0.720904 0.875773 0.760982
R>