title: how do I get rid of random background grid from arrangeGrob
body: <p>I need to wrap several plots in a grid, often an uneven number, <strong>so there'll often be an "empty spot"</strong>.
  I need to use <code>arrangeGrob()</code> -- not <code>grid.arrange()</code> -- because I want to save the plot for later, not <code>plot()</code> it right away.</p>
  
  <p>This works fine, but oddly, <code>arrangeGrob()</code> leaves some weird background in the empty spots.</p>
  
  <p>Like so:</p>
  
  <pre><code>library(ggplot2)
  p1 &lt;- ggplot(mtcars, aes(x=factor(cyl), y=mpg)) + geom_boxplot()
  p2 &lt;- ggplot(mtcars, aes(x=factor(cyl), y=wt)) + geom_boxplot()
  p3 &lt;- ggplot(mtcars, aes(x =factor(cyl), y=disp)) + geom_boxplot()
  library(gridExtra)
  y &lt;- arrangeGrob(p1, p2, p3, ncol = 2)
  plot(y)
  </code></pre>
  
  <p>yields a plot with some weird gray stuff in the bottom right corner:</p>
  
  <p><img src="https://i.stack.imgur.com/yGLPj.png" alt="grey weirdness"></p>
  
  <p>Compare this to <code>grid.arrange()</code>:</p>
  
  <pre><code>grid.arrange(p1, p2, p3, ncol = 2)
  </code></pre>
  
  <p>yields a pretty plot with no grey weirdness:</p>
  
  <p><img src="https://i.stack.imgur.com/Um9vT.png" alt="enter image description here"></p>
  
  <p>Where does this gray stuff in the bottom right corner come from? And how do I get rid of it?</p>
  
  <p>Notice that <strong>I cannot avoid the empty spots</strong> by changing <code>ncol</code>; I sometimes <strong>have an uneven number of plots</strong>, so there'll always be empty spots.
  I'm ok with empty spots, I just like them to be clean.
  (In isolation, that last sentence sounds pretty <a href="https://en.wikipedia.org/wiki/Obsessive%E2%80%93compulsive_disorder" rel="nofollow noreferrer">OCD-ish</a>.</p>
  
  <hr>
  
  <p><strong>UPDATE</strong></p>
  
  <p>The package author (?) answered below: I should have used <code>grid.draw(y)</code>.</p>
  
  <p>A similar problem remains (maybe the same root cause?): if you plot <em>some</em> object before, the "empty spot" remains occupied by that <em>past</em> plot.
  Weird.
  Like so:</p>
  
  <pre><code>plot(p1)
  grid.draw(y)
  </code></pre>
  
  <p>yields:</p>
  
  <p><img src="https://i.stack.imgur.com/KYWui.png" alt="past plot weirdness"></p>