Some features of the %dorng% foreach operator

  
library(doRNG)
library(doParallel)
registerDoParallel(cores=2)
# single %dorng% loops are reproducible
r1 <- foreach(i=1:4, .options.RNG=1234) %dorng% { runif(1) }
r2 <- foreach(i=1:4, .options.RNG=1234) %dorng% { runif(1) }
identical(r1, r2)

[1] TRUE
# the sequence os RNG seed is stored as an attribute
attr(r1, 'rng')

[[1]]
[1]         407  -305383241    69318028 -1161659107  -348804806 -1127582349  -343284712

[[2]]
[1]         407  1222430165 -1386318120  1144759979   748500427   690571908   329037778

[[3]]
[1]         407   215137210 -1421031558  1452323561 -2060097535   712279522  -278425444

[[4]]
[1]         407 -1017432992  1583835527  1997665660   821136125  1282044776  1045008570

# sequences of %dorng% loops are reproducible
set.seed(1234)
s1 <- foreach(i=1:4) %dorng% { runif(1) }
s2 <- foreach(i=1:4) %dorng% { runif(1) }
# two consecutive (unseed) %dorng% loops are not identical
identical(s1, s2)

[1] FALSE
# But the whole sequence of loops is reproducible
set.seed(1234)
s1.2 <- foreach(i=1:4) %dorng% { runif(1) }
s2.2 <- foreach(i=1:4) %dorng% { runif(1) }
identical(s1, s1.2) && identical(s2, s2.2)

[1] TRUE
# it gives the same result as with .options.RNG
identical(r1, s1)

[1] TRUE
# Works with SNOW-like and MPI clusters
# SNOW-like cluster
cl <- makeCluster(2)
registerDoParallel(cl)
s1 <- foreach(i=1:4, .options.RNG=1234) %dorng% { runif(1) }
s2 <- foreach(i=1:4, .options.RNG=1234) %dorng% { runif(1) }
identical(s1, s2)

[1] TRUE
stopCluster(cl)
registerDoSEQ()
# MPI cluster
library(doMPI)

Loading required package: Rmpi
cl <- startMPIcluster(2)

	2 slaves are spawned successfully. 0 failed.
registerDoMPI(cl)
s1 <- foreach(i=1:4, .options.RNG=1234) %dorng% { runif(1) }
s2 <- foreach(i=1:4, .options.RNG=1234) %dorng% { runif(1) }
identical(s1, s2)

[1] TRUE
closeCluster(cl)
registerDoSEQ()