title: Nested facet plot with ggplot2
body: <p>If I have a nested factor, in this case I have multiple "Family" levels that are contained in the factor "Order", I would like to potentially create a  </p>
  
  <pre><code>facet_grid(Family / Order ~.)
  </code></pre>
  
  <p>instead of the current </p>
  
  <pre><code>facet_grid(Family + Order ~.) 
  </code></pre>
  
  <p>Basically -- ONE strip for every Order -- that contains next to it all strips for each family inside that Order.  I know that facet_grid(Family / Order ~.) is currently not possible, but how would I achieve this effect?  Could it be done with a theme()?  Thank you so much.  --SB</p>
  
  <p>I should have specified above that both Family and Order are factors.  The data values B are by Species which have a Family level and Order level they belong to.  Here is the code for my plot: </p>
  
  <pre><code>p &lt;- ggplot(models, aes(B,Species)) + geom_point() + facet_grid(Family + Order ~
   .,scales="free",space="free")
  </code></pre>
  
  <p>Here is some sample data:</p>
  
  <pre><code>structure(list(Species = c("Acanthocyclops robustus", "Acroperus harpae", 
  "Alona affinis", "Ascaphus truei", "Bosmina longirostris"), Intercept = c(-36.1182388331068, 
  -27.2140776216155, -25.7920464721491, -39.2233884219763, -31.4301301084581
  ), B = c(0.919397836908493, 0.716601987210452, 0.685455190113372, 
  1.04159758611351, 0.81077051300147), Bconf = c(0.407917065756464, 
  0.181611850119198, 0.254101713856315, 0.708582768458448, 0.234313394549538
  ), Order = c("Cyclopoida", "Diplostraca", "Diplostraca", "Anura", 
  "Diplostraca"), Family = c("Cyclopidae", "Chydoridae", "Chydoridae", 
  "Leiopelmatidae", "Bosminidae")), .Names = c("Species", "Intercept", 
  "B", "Bconf", "Order", "Family"), row.names = c(NA, 5L), class = "data.frame")
  </code></pre>