R set.seed() 's scope

Question

My R script calls sub-functions which contains set.seed(). What is the scope of the set.seed()? Will it also affect to main program that calls it?

More specificly

# main program
callsubfun()

... some statement ...

sample.int(100,20)



# sub function
callsubfun <- function(x,y,...){
   set.seed(100)
   ... do the work ...
   return(something)
}

Answer 1

set.seed is indeed global. But note this from the example in ?set.seed:

## If there is no seed, a "random" new one is created:
rm(.Random.seed); runif(1); .Random.seed[1:6]

This means you can call rm(.Random.seed, envir=.GlobalEnv) either at the end of your function or after you call the function to decouple the rest of the program from the call to set.seed in the function.

To see this in action, run the following code in two different R sessions. The outputs should be the same in both sessions. Then re-run the code again in two new R sessions with the rm line uncommented. You'll see the output in the two new sessions now differ, indicating that the call to set.seed in the function hasn't transferred the reproducibility to the main program.

subfun <- function() {
    set.seed(100)
    rnorm(1)
    #rm(.Random.seed, envir=.GlobalEnv)
}

subfun()
#[1] -0.5022

rnorm(1)
# [1] 0.1315