Can I get.seed() somehow?

Question

In reference to the statement set.seed(), can I get the seed instead after running some code if I didn\'t set it explicitly?

I\'ve been re-running some

Answer 1

If you didn't keep the seed, there's no general way to "roll back" the random number generator to a previous state after you've observed a random draw. Going forward, what you may want to do is save the value of .Random.seed along with the results of your computations. Something like this.

x <- .Random.seed
result <- <your code goes here>
attr(result, "seed") <- x

Then you can reset the PRNG as follows; result2 should be the same as result.

.Random.seed <- attr(result, "seed")
result2 <- <your code goes here>

Answer 2

To add to the answer mpettis gave, if you don't want to re-execute the script manually--generating new random seeds each iteration--you could do something like this:

# generate vector of seeds
eff_seeds <- sample(1:2^15, runs)

# perform 'runs' number of executions of your code
for(i in 1:runs) {
    print(sprintf("Seed for this run: %s", eff_seeds[i]))
    set.seed(eff_seeds[i])

    # your code here
    # don't forget to save your outputs somehow
}

Where the variable 'runs' is a positive integer indicating the number of times you want to run your code.

This way you can generate a lot of output rapidly and have individual seeds for each iteration for reproducibility.

Answer 3

> rnorm(5)
[1] -0.17220331 -0.31506128 -0.35264299  0.07259645 -0.15518961
> Seed<-.Random.seed
> rnorm(5)
[1] -0.64965000  0.04787513 -0.14967549  0.12026774 -0.10934254
> set.seed(1234)
> rnorm(5)
[1] -1.2070657  0.2774292  1.0844412 -2.3456977  0.4291247
> .Random.seed<-Seed
> rnorm(5)
[1] -0.64965000  0.04787513 -0.14967549  0.12026774 -0.10934254

Answer 4

Hong's answer above is robust. For quick and dirty solutions, where I just re-execute a whole script until I get interesting behavior, I randomly pick an integer, print it out, then use that as a seed. If my particular run has interesting behavior, I note that seed:

eff_seed <- sample(1:2^15, 1)
print(sprintf("Seed for session: %s", eff_seed))
set.seed(eff_seed)