如何并行两个或多个函数

Question

If I have two or more functions with different parameters,how can I make them parallel? Please give me an example that is not too complicated.

I only know how to parallel single function.

 test <- function(x) {
     for (i in 1:10000000) {
         x <- x + i
     }
     return(x)
 }
 library(snow)
 cl <- makeCluster(type = "SOCK", c("localhost", "localhost"))  # 建立两个本地CPU内核的并行
 system.time({test(5);test(5)})
用户 系统 流逝 
0.58 0.00 0.58 
 system.time(clusterCall(cl, test,5)) # 测试并行循环的耗时
用户 系统 流逝 
0.00 0.00 0.37 

Answer 1

How about using library foreach ?

First install foreach and doParallel

install.packages('foreach')
install.packages('doParallel')

And i edited your code a litte .

test1 <- function(x) {
 for (i in 1:10000000) {
 x <- x + i
 }
 return(x)
}
library(snow)
cl <- makeCluster(type = "SOCK", c("localhost", "localhost")) 
doParallel::registerDoParallel(cl)

If you have functions like test1, test2, test3, ...

After registerDoParallel , you can use any another function you want like below.

foreach::foreach(i=1:2) %dopar% {
test1(x)
test2(x)
test3(x)
...
}