[R] .Random.seed

[Sundar Dorai-Raj]

This is a scoping issue. I think what you want in your example is

test <-  function(runs, seed) {
   # this is a local copy of ".Random.seed"
   .Random.seed <- seed
   # need to make a global copy
   assign(".Random.seed", .Random.seed, 1)
   for (i in 1:runs) {
     print(i)
     print(runif(1,0,1))
     print(.Random.seed)
   }
   return(.Random.seed)
}

RNGkind(kind="Marsaglia-Multicarry")
set.seed(20391)
seed1 <- .Random.seed
seed1
test(2, seed1)
test(2, seed1)


Hope this helps,

-sundar

Ann Hess wrote:
> I am writing a function for the purposes of a simulation.  Due to memory
> problems, the function sometimes crashes.  In order to get around this
> problem, I would like to include to be able to save the "last" seed, so I
> can pick up with the next run of the simulation after a "crash".  I am
> having trouble understanding what is going on with .Random.seed!
> 
> For each run of the following function, a random uniform and the current
> .Random.seed should be printed:
> 
> test<-function(runs,seed){
>    .Random.seed<-seed
>    for (i in 1:runs) {
> print(i)
> print(runif(1,0,1))
> print(.Random.seed)}
>    return(.Random.seed}
> 
> Consider the following input/output:
> 
>>RNGkind(kind="Marsaglia-Multicarry")
>>set.seed(20391)
>>seed1<-.Random.seed
>>seed1
> 
> [1]         401 -1607331462  -462081869
> 
>>test(2,seed1)
> 
> [1] 1
> [1] 0.4188851
> [1]         401 -1607331462  -462081869
> [1] 2
> [1] 0.7713649
> [1]         401 -1607331462  -462081869
> [1]         401 -1607331462  -462081869
> 
>>seed1
> 
> [1]         401 -1607331462  -462081869
> 
>>test(2,seed1)
> 
> [1] 1
> [1] 0.7293294
> [1]         401 -1607331462  -462081869
> [1] 2
> [1] 0.8266798
> [1]         401 -1607331462  -462081869
> [1]         401 -1607331462  -462081869
> 
> 
> The output from each call of the function seems to suggest that
> .Random.seed is not changing (although different random uniforms are
> generated each time).  The second call of the function doesn't match the
> first call even though the same "seed" is used.
> 
> Can anyone explain what is happening here?  My goal is to save the "last"
> seed so that I can use it to generate the next run of a simulation (after
> a crash).
> 
> Thanks in advance!
> 
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