packages_installed <- function(pkg_list){
pkgs <- unlist(pkg_list)
req <- unlist(lapply(pkgs, require, character.only = TRUE))
not_installed <- pkgs[req == FALSE]
lapply(not_installed, install.packages,
repos = "http://cran.r-project.org")# add lib.loc if needed
lapply(pkgs, library, character.only = TRUE)
}