Example code to parallelize R with plyr and doMC

parallel_example.R

# Parallelize R
# Source: http://blog.yhat.com/posts/running-r-in-parallel.html

library(plyr)
library(doMC)

# set number of cores (mine has two cores)
doMC::registerDoMC(cores = 2) # number of cores you have access to

# Process data

# don't parallelize
system.time(ddply(iris, .(Species), function(x) {
    Sys.sleep(2)
    nrow(x)
}))
#  user  system elapsed 
# 0.030   0.022   6.015 

# parallelize
system.time(ddply(iris, .(Species), function(x) {
    Sys.sleep(2)
    nrow(x)
}, .parallel = TRUE))
#  user  system elapsed 
# 0.016   0.025   4.033