Function to (install and) load all required packages

install_load_all.R

install_load_all <- function(x) {
  .install_load_all <- function(x) {
    if(!require(x, character.only = TRUE)) {
      install.packages(x, repos = "http://cran.us.r-project.org")
      library(x, character.only = TRUE)
    }
  }
  
  invisible(sapply(x, .install_load_all))
}