title: accessing Global Environment dataframe in knitr
body: <p>I have a dataframe in R called <code>df</code>. This is available across all .r files in the R session. I want to <em>knitr</em> some of the results from this dataframe into a .Rmd file. I'm using the following code:</p>
  
  <pre><code>```{r}
  names(df)
  ```
  </code></pre>
  
  <p>If I highlight and run the line: <code>names(df)</code> within the .Rmd file, it correctly prints out the names of <code>df</code>: <code>[1] "ISIN" "CF"   "DATE"</code>. But if I click on <code>Knit HTML</code>, it outputs in HTML:</p>
  
  <pre><code>## NULL
  </code></pre>
  
  <p>How do I get a .Rmd document to access Global Environment variables?</p>