title: R environment variable not clearing markdown
body: <p>I started using the below code in my scripts to clear the environment before every run.</p>
  
  <pre><code># Clear environment
  rm(list = ls())
  </code></pre>
  
  <p>This works great in R scripts.
  However, when I Knit the below RMarkdown document in RStudio, my environment variables are not clearing. </p>
  
  <p>To test, run <code>myNewVariable &lt;- 2</code> in the console, then Knit the below RMarkdown document. When I do this, myNewVariable still exists. Is this normal?</p>
  
  <pre><code>---
  title: "Clear Environment"
  author: "John"
  date: "August 17, 2015"
  output: html_document
  ---
  
  ```{r}  
  # Clear environment
  rm(list = ls())
  ```
  </code></pre>