title: ggplot2: suppress drawing of plot when calling print method
body: <p>As a follow up to <a href="https://stackoverflow.com/questions/12828125/ggplot2-reading-maximum-bar-height-from-plot-object-containing-geom-histogram">this question</a>, suppose I do something like this:</p>
  
  <pre><code>p &lt;- ggplot(mtcars, aes(mpg)) + geom_histogram(aes(y = ..count..)) + facet_wrap(~am)
  r &lt;- print(p)
  </code></pre>
  
  <p>In the second line I'm calling the print method just so that I can programmatically inspect its return value before adding additional layers to the plot object. </p>
  
  <p>My question: Is there a way to suppress drawing the plot at that point?</p>