install.packages("foreach")
install.packages("doSNOW")

library(foreach)
#we get result as list
foreach(i = 1:3) %do% {sqrt(i)}
#we get result as vector with using .combine="c" option
foreach(i = 1:3,.combine = "c") %do% {sqrt(i)}
#if a result is "vector",we can get it as matrix with using .combine="cbind" option
foreach(i = 1:3,.combine = "cbind") %do% {letters[1:4]}
#if you define a function,you can use it as .combine option
#I wrote my function as returning same result that specify .combine="c" 
MyFunc <- function(x,y)c(x,y)
foreach(i = 1:3, .combine = "MyFunc") %do% {
  sqrt(i)
}

> library(doSNOW)
> getDoParWorkers()
[1] 1
> getDoParName()
NULL
> registerDoSNOW(makeCluster(2, type = "SOCK"))
> getDoParWorkers()
[1] 2
> getDoParName()
[1] "doSNOW"
> getDoParVersion()
[1] "1.0.3"

> N <- 10^4
> system.time(foreach(i = 1:N,.combine = "cbind") %do% {
+   sum(rnorm(N))
+ })
   ユーザ   システム       経過
     57.52       0.48      59.60
> system.time(foreach(i = 1:N,.combine = "cbind") %dopar% {
+   sum(rnorm(N))
+ })
   ユーザ   システム       経過
     18.61       0.58      37.74