title: Prevent chunk evaluation in R Notebook interactive
body: <p>Using the chunk option <code>eval=FALSE</code> one can suppress chunk evaluation in an RMarkdown file or R Notebook when it is knit. Is there a way to make this apply during interactive running of the document in RStudio (i.e., making "run all chunks" skip certain chunks)?</p>
  
  <p>I've got some chunks in the beginning of my analysis that take a while to run, which the later sections don't depend on. I want to be able to source the important parts of the code so I can continue writing the downstream stuff, without having to do it manually chunk-by-chunk so I can avoid the parts I don't need in my workspace for further writing.</p>
  
  <p>I've set up the rmarkdown document with logical parameters meant to change which parts of the code need to get run - I meant these as control flags for when the code is actually finished and getting used, but I was hoping I could use those same parameters to exclude chunks from running in interactive mode (i.e., something like <code>eval=params$run_part1</code>).</p>