incl/doFuture.R

In HenrikBengtsson/doFuture: Use Foreach to Parallelize via the Future Framework

\donttest{
library(iterators)  # iter()
registerDoFuture()  # (a) tell %dopar% to use the future framework
plan(multisession)  # (b) parallelize futures on the local machine


## Example 1
A <- matrix(rnorm(100^2), nrow = 100)
B <- t(A)

y1 <- apply(B, MARGIN = 2L, FUN = function(b) {
  A %*% b
})

y2 <- foreach(b = iter(B, by = "col"), .combine = cbind) %dopar% {
  A %*% b
}
stopifnot(all.equal(y2, y1))



## Example 2 - Chunking (4 elements per future [= worker])
y3 <- foreach(b = iter(B, by = "col"), .combine = cbind,
              .options.future = list(chunk.size = 10)) %dopar% {
  A %*% b
}
stopifnot(all.equal(y3, y1))


## Example 3 - Simulation with parallel RNG
library(doRNG)

my_stat <- function(x) {
  median(x)
}

my_experiment <- function(n, mu = 0.0, sigma = 1.0) {
  ## Important: use %dorng% whenever random numbers
  ##            are involved in parallel evaluation
  foreach(i = 1:n) %dorng% {
    x <- rnorm(i, mean = mu, sd = sigma)
    list(mu = mean(x), sigma = sd(x), own = my_stat(x))
  }
}

## Reproducible results when using the same RNG seed
set.seed(0xBEEF)
y1 <- my_experiment(n = 3)

set.seed(0xBEEF)
y2 <- my_experiment(n = 3)

stopifnot(identical(y2, y1))

## But only then
y3 <- my_experiment(n = 3)
str(y3)
stopifnot(!identical(y3, y1))

}

\dontshow{
## R CMD check: make sure any open connections are closed afterward
if (!inherits(plan(), "sequential")) plan(sequential)
}