title: Suppress comment (#) when eval=FALSE in RMarkdown
body: <p>I want to use a lengthy data frame, but only display part of it in my slides.</p>
  
  <pre><code>```{r}
  df1 = data.frame(x = rnorm(100), y = rnorm(100))
  df1
  ```
  </code></pre>
  
  <p>As you might guess, this produces output that won't fit in a presentation slide.</p>
  
  <pre><code>```{r eval=-2, echo=-3}
  df1 = data.frame(x = rnorm(100), y = rnorm(100))
  df1
  head(df1)
  ```
  </code></pre>
  
  <p>This produces:</p>
  
  <pre><code>df1 = data.frame(x = rnorm(100), y = rnorm(100))
  ## df1
  
  x       y
  1  0.7699 -0.1683
  2 -0.4756  0.3885
  3 -0.6744  1.2755
  4 -0.8533 -2.1271
  5 -1.9129 -1.2661
  6 -0.4567  0.5607
  </code></pre>
  
  <p>But I don't want the second code line to be commented out. At the moment, the only way I can figure out to do this is in two separate code chunks, because <code>eval=FALSE</code> does not result in commented code when it applies to the whole chunk.</p>
  
  <p>This produces what I want:</p>
  
  <pre><code>```{r eval=FALSE}
  df1 = data.frame(x = rnorm(100), y = rnorm(100))
  df1
  ```
  
  ```{r echo=FALSE}
  df1 = data.frame(x = rnorm(100), y = rnorm(100))
  head(df1)
  ```
  </code></pre>
  
  <p>But obviously, if I change the code, I have to change it in two places. This is a simple example, but for more complex code, there is a greater danger of my code and results becoming out of sync as I edit it.</p>