[Rd] Best way to reset random seed when using set.seed() in a function?

[Henrik Bengtsson]

On Feb 13, 2008 11:07 AM, Paul Gilbert <pgilbert at bank-banque-canada.ca> wrote:
> I think in general it is a good idea to use  on.exit()  to reset the
> seed if you mess with it. Otherwise you can generate unintended
> consequences for other programs. Something like:
>     old.seed <- setRNG(kind = "default", seed = test.seed, normal.kind =
> "default")
>     on.exit(setRNG(old.seed))

Yes, agree; on.exit() should always be used when you want to cleanup
after yourself.  Much better.

>
> (BTW, setRNG is a simple little utility in the setRNG package, to help
> set and save some of the other things you need besides the seed, if you
> are going to try to reproduce results.)

Thanks for this note.  This seems much more natural to work with than
'.Random.seed'.

/Henrik


>
> Paul
>
>
> Henrik Bengtsson wrote:
> > Hi,
> >
> > this is related to a question just raised on Bioconductor where one
> > function sets the random seed internally but never resets it, which
> > results in enforced down streams random samples being deterministic.
> >
> > What is the best way to reset the random seed when you use set.seed()
> > within a function?  Is it still to re-assign '.Random.seed' in the
> > global environment as following example illustrates?  I'm not too kind
> > of having function modifying the global environment, if not really
> > necessary.
> >
> > foo <- function(n) {
> >   # Pop random seed
> >   if (!exists(".Random.seed", mode="numeric"))
> >     sample(NA);
> >   oldSeed <- .Random.seed;
> >
> >   # Fixed seed to get reproducible samples here
> >   set.seed(0xbeef);
> >   x <- sample(5);
> >
> >   # Proof of concept: 'x' should be the same all the time
> >   stopifnot(identical( x, as.integer(c(4,2,5,1,3)) ));
> >
> >   # Push random seed to old state
> >   assign(".Random.seed", oldSeed, envir=globalenv())
> >
> >   # Continue as nothing happened
> >   sample(n);
> > }
> >
> >
> >> foo(5)
> >>
> > [1] 4 2 3 5 1
> >
> >> foo(5)
> >>
> > [1] 4 2 3 1 5
> >
> >> foo(5)
> >>
> > [1] 5 3 1 4 2
> >
> >> foo(5)
> >>
> > [1] 5 3 2 4 1
> >
> >> foo(5)
> >>
> >
> > Is this the way to do it?
> >
> > Thanks
> >
> > Henrik
> >
> > ______________________________________________
> > R-devel at r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-devel
> >
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