Install and load multiple R packages at once

ipak.R

# 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.
# Forked from: https://gist.github.com/stevenworthington/3178163

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

# usage
# packages <- c("ggplot2", "plyr", "reshape2", "RColorBrewer", "scales", "grid")
# ipak(packages)