Tycho-1

# restore_packages.R
#
# installs each package from the stored list of packages
# source: http://hlplab.wordpress.com/2012/06/01/transferring-installed-packages-between-different-installations-of-r/

load("~/installed_packages.rda")

for (count in 1:length(installedpackages)) {
    install.packages(installedpackages[count])
}

Tycho-1

# ipak function: install and load multiple R packages.
# check to see if packages are installed. Install them if they are not, then load them into the R session.

ipak <- function(pkg){
    new.pkg <- pkg[!(pkg %in% installed.packages()[, "Package"])]
    if (length(new.pkg)) 
        install.packages(new.pkg, dependencies = TRUE)
    sapply(pkg, require, character.only = TRUE)
}