Open
Description
Issue
library(future.apply)
y <- do.call(rbind, future_lapply(1:3, future.seed = TRUE, FUN = function(i) {
do.call(rbind, future_lapply(1:3, future.seed = TRUE, FUN = function(j) {
data.frame(i = i, j = j, random = runif(n = 1L)) }))
})
)
print(y)gives
i j random
1 1 1 0.8146860
2 1 2 0.4950540
3 1 3 0.9308272
4 2 1 0.4950540
5 2 2 0.9308272
6 2 3 0.2019456
7 3 1 0.9308272
8 3 2 0.2019456
9 3 3 0.6057787Note how some of the random numbers are duplicated, e.g.
> y$random
[1] 0.8146860 0.4950540 0.9308272 0.4950540 0.9308272 0.2019456 0.9308272
[8] 0.2019456 0.6057787
> unique(y$random)
[1] 0.8146860 0.4950540 0.9308272 0.2019456 0.6057787Troubleshooting
It could be that we've been here before; this seems familiar. I don't have time to investigate in full right now, but it's not that the RNG state of the parent isn't forwarded;
> seed0 <- .Random.seed
> y <- future_lapply(1:3, FUN = function(i) runif(n = 1L), future.seed = TRUE)
> seed <- .Random.seed
> identical(seed, seed0)
[1] FALSEbut it could be that it's only forwarded a single step, whereas it needs to be forward length(X) steps.