title: Change the axes on a radial barchart
body: <p>I want to make a radial stacked barchart. I have something like this:</p>
  
  <pre><code>ggplot(diamonds, aes(clarity, fill= cut)) +  geom_bar()  + coord_polar()
  </code></pre>
  
  <p>which yields a plot like this:
  <img src="https://i.stack.imgur.com/25lu7.png" alt="radial barchart"></p>
  
  <p>However this is very crowded. Is there a way to change the axes so that this barchart is hollow? I would want zero to start not at the center of the circle but, say, 1/3  or 1/2 of the radius from the center. Any ideas about that?</p>