title: positioning horizontal boxplots in ggplot2
body: <p>I'm trying to make a plot with horizontal boxplots in ggplot2, which you can only do by using coord_flip(). I'm also trying to space the boxplots vertically to group certain sets together. I have read that faceting is recommended for this kind of thing, but this is incompatible with coord_flip(), as we can see here: <a href="https://stackoverflow.com/questions/10735539/ggplot2-boxplot-with-facet-grid-and-free-scale">ggplot2: boxplot with facet_grid and free scale</a>. So I'm wondering if it's possible to use blank levels in order to create blank spaces. Here's what I've managed to do so far:</p>
  
  <pre><code>d &lt;- diamonds
  library("ggplot2")
  levels(d$cut) &lt;- list(A="Fair", B="Good", "-", C="Very Good", D="Ideal", E="Premium")
  p = ggplot(d, aes(x=cut, y=depth))
  p + 
      geom_boxplot(color="black", size=0.2) + 
      theme_bw() + 
      scale_x_discrete(breaks = c("A", "B", "-", "C", "D", "E"), drop=FALSE) +
      coord_flip()
  
  ph = 2.75
  pw = 4
  ggsave("plot.png", height=ph, width=pw)
  </code></pre>
  
  <p>As you can see, if I create a blank level with "-" in it and include it in scale_x_discrete(), then somehow I get a blank row. The problem is I can only add one space. Does anyone have any ideas on how to add spaces between these horizontal box plots?</p>