Wrapper for install.packages() to install an R package only if necessary (checks library and, if installed, current package version)

install_if_needed

install_if_needed <- function(pkgs, lib=NULL, repos=getOption("repos"),
  contriburl=contrib.url(repos, type), method, available=NULL, destdir=NULL, 
  dependencies=NA, type=getOption("pkgType"), configure.args=getOption("configure.args"), 
  configure.vars=getOption("configure.vars"), clean=FALSE, Ncpus=getOption("Ncpus", 1L), 
  verbose = getOption("verbose"), libs_only=FALSE, INSTALL_opts, quiet=FALSE, 
  keep_outputs=FALSE, 
  check_version=TRUE, 
  ...)
{
  installed <- installed.packages()
  installed <- data.frame(Package=installed[, "Package"], Version=installed[, "Version"], stringsAsFactors=FALSE)
  
  avail <- available.packages()
  avail <- data.frame(Package=avail[, "Package"], Version=avail[, "Version"], stringsAsFactors=FALSE)
  
  for (pkg in pkgs)
  {
    if (any(installed$Package == pkg))
    {
      if (check_version)
      {
        installed.version <- installed[which(installed$Package == pkg), 2]
        avail.version <- avail[which(avail$Package == pkg), 2]
        
        if (installed.version != avail.version)
          should.install <- TRUE
        else
          should.install <- FALSE
      }
    }
    else
      should.install <- TRUE
    
    if (should.install)
    {
      install.packages(pkgs=pkg, lib=lib, repos=repos, contriburl=contriburl, method=method,
        available=available, destdir=destdir, dependencies=dependencies, type=type,
        configure.args=configure.args, configure.vars=configure.vars, clean=clean,
        Ncpus=Ncpus, verbose=verbose, libs_only=libs_only, INSTALL_opts=INSTALL_opts,
        quiet=quiet, keep_outputs=keep_outputs, ...)
    }
    else
      warning(paste("Skipping", pkg))
  }
  
  invisible()
}