title: Compile an older R version and switch between versions in Ubuntu and RStudio
body: <p>I just made the switch from Windows to Ubuntu. In windows I had the possibility to change the R version used in Rstudio IDE with Tools -> Global options -> R versions. </p>
  
  <p>This is not possible in Ubuntu in the same way, indeed the R versions menu does not appear in Ubuntu version of RStudio (why??). Could you help me in finding the good solution for switching among different, already installed versions of R, in Ubuntu? </p>
  
  <p>The switch among different versions is important for satisfying packages modifications and making old scripts working.</p>