This is something that I've occassionally wanted to do - and haven't yet come up with much better than the following kludge (which is only really useful if you're using just 1 or 2 different random distributions, as you have to write a function for each:
#Make a list of seeds - generalises to mkore than 2
seed <- list(NA,NA)
set.seed(1)
seed[[1]] <- .Random.seed
set.seed(2)
seed[[2]] <- .Random.seed
my_runif <- function(...,which.seed=1)
{
.Random.seed <<- seed[[which.seed]]
x <-runif(...)
seed[[which.seed]] <<- .Random.seed
x
}
##Print some data for comparison
> set.seed(1); runif(10)
[1] 0.26550866 0.37212390 0.57285336 0.90820779 0.20168193 0.89838968 0.94467527 0.66079779 0.629114040.06178627
> set.seed(2); runif(10)
[1] 0.1848823 0.7023740 0.5733263 0.1680519 0.9438393 0.9434750 0.1291590 0.8334488 0.4680185 0.5499837
#Test
> my_runif(1,which.seed=1)
[1] 0.2655087
> my_runif(1,which.seed=1)
[1] 0.3721239
> my_runif(1,which.seed=1)
[1] 0.5728534
> my_runif(1,which.seed=2)
[1] 0.1848823
> my_runif(1,which.seed=1)
[1] 0.9082078
I'd imagine that the <<- will break if you call my_runif from inside another function.
fortunes::fortune("<<-")
ETA:
The following might be more robust
my_runif <- function(...,which.seed=1)
{
assign(".Random.seed", seed[[which.seed]], envir = .GlobalEnv)
x <-runif(...)
seed <- seed #Bring into local envir
seed[[which.seed]] <- .Random.seed
assign("seed", seed, envir = .GlobalEnv)
x
}
