title: Polar coordinate / circular layout for the whole facet_grid
body: <p>I have a dataset with values 2 ordered discrete factors, with some corresponding continuous values. (random sample is generated below)</p>
  
  <pre><code>randomData = expand.grid(1:5, 1:100)    # The two discrete variables
  colnames(randomData) = c("index1", "index2")
  
  randomData$z = runif(nrow(randomData))   # The measured value 
  
  ggplot(randomData, aes(x = 1, y = z)) + 
    geom_bar(stat = "identity") + 
    facet_grid(index1 ~ index2) + 
    theme_minimal()
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/Zvqo8.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Zvqo8.png" alt="enter image description here"></a></p>
  
  <p>I am trying to wrap the whole grid into circular / polar layout, such as the one displayed below, using the bar plots generated.</p>
  
  <p>The first plot is the desired output (manipulated by a photo editing tool from the first facet plot).
  The second plot is the output of this blog post: <a href="http://chrisladroue.com/2012/02/polar-histogram-pretty-and-useful/" rel="nofollow noreferrer">http://chrisladroue.com/2012/02/polar-histogram-pretty-and-useful/</a>). However, it contains only a single "row". </p>
  
  <p><a href="https://i.stack.imgur.com/NSk2v.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/NSk2v.png" alt="enter image description here"></a> 
  <a href="https://i.stack.imgur.com/9CFsM.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/9CFsM.png" alt="enter image description here"></a></p>
  
  <p>I cant figure out a way to do that. when I try to add <code>coord_polar()</code>, the bar plots themselves are affected and not the facet. </p>