[R] Restoring .Random.seed

[Prof Brian Ripley]

On Thu, 31 May 2007, Talbot Katz wrote:

> Hi.
>
> Suppose I have a function which does some random number generation within.
> The random number generation inside the function changes the value of
> .Random.seed in the calling environment.  If I want to restore the
                ^^^^^^^^^^^^^^^^^^^^^^^^^^
That is your misunderstanding.  From the help page

      The object '.Random.seed' is only looked for in the user's
      workspace.

which seems plain enough.  So, you can do

save.seed <- get(".Random.seed", .GlobalEnv)
assign(".Randon.seed", save.seed, .GlobalEnv)

to save and restore, *provided* that random numbers have been used in the 
session (or .Random.seed will not exist).

However, the help recommends using set.seed(), and why not follow the 
advice?

> pre-function call .Random.seed, I can do:
>
> save.seed<-.Random.seed
> result<-myfunction()
> .Random.seed<-save.seed
>
> Is there a way to do the restoration inside the function?  I tried putting
> the "save.seed<-.Random.seed" and ".Random.seed<-save.seed" statements
> inside the function, but that didn't work.

As documented on the help page.

[...]

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595