Checks if multiple R packages are installed. If yes, they are required. If not, they are installed and required.

load_packages.R

load.package <- function(package, repos) {

  # list of packages missing
  missing <- package[!package %in% installed.packages()[, 'Package']]

  # check wich packages are not intalled and install them
  if (!is.null(missing)) {
    if (missing(repos)) {
      # use Goettingen (Germany) mirror as default
      repos <- 'https://ftp.gwdg.de/pub/misc/cran/'
    }
    install.packages(missing, dependencies = TRUE,
                     repos = repos)
  }

  # load all packages
  sapply(package, require, character.only = TRUE)
}