Checks for package installation. If the package does not exist, it installs them.

InstallPackages.R

needed = c("lubridate", "dplyr", "data.table", "stringr")

is.installed = function(pkg){
  is.element(pkg, installed.packages()[,1])
} 

# For loop to run through each of the packages
for (p in 1:length(needed)){
  ifelse(!is.installed(needed[p]), install.packages(needed[p], dependencies = T), print(paste(needed[p], " is already installed", sep = "")))
}