setting seed locally (not globally) in R

Question

I'd like to set seeds in R only locally (inside functions), but it seems that R sets seeds not only locally, but also globally. Here's a simple example of what I'm trying (not) to do.

myfunction <- function () {   set.seed(2) }  # now, whenever I run the two commands below I'll get the same answer myfunction() runif(1) 

So, my questions are: why does R set the seed globally and not only inside my function? And how I can make R to set the seed only inside my function?

Answer 1

Something like this does it for me:

myfunction <- function () {   old <- .Random.seed   set.seed(2)   res <- runif(1)   .Random.seed <<- old   res } 

Or perhaps more elegantly:

myfunction <- function () {   old <- .Random.seed   on.exit( { .Random.seed <<- old } )   set.seed(2)   runif(1) } 

For example:

> myfunction() [1] 0.1848823 > runif(1) [1] 0.3472722 > myfunction() [1] 0.1848823 > runif(1) [1] 0.4887732