title: Set categorical axis labels with scales "free" ggplot2
body: <p>I am trying to set the labels on a categorical axis within a faceted plot using the ggplot2 package (1.0.1) in R (3.1.1) with scales="free". If I plot without  manually setting the axis tick labels they appear correctly (first plot), but when I try to set the labels (second plot) only the first n labels are used on both facets (not in sequence as with the original labels).</p>
  
  <p>Here is a reproducible code snippet exemplifying the problem:</p>
  
  <pre><code>foo &lt;- data.frame(yVal=factor(letters[1:8]), xVal=factor(rep(1:4,2)), fillVal=rnorm(8), facetVar=rep(1:2,each=4))
  ## axis labels are correct
  p &lt;- ggplot(foo) + geom_tile(aes(x=xVal, y=yVal, fill=fillVal)) + facet_grid(facetVar ~ ., scales='free')
  print(p)
  ## axis labels are not set correctly
  p &lt;- p + scale_y_discrete(labels=c('a','a','b','b','c','d','d','d'))
  print(p)
  </code></pre>
  
  <p>I note that I cannot set the labels correctly within the data.frame as they are not unique. Also I am aware that I can accomplish this with arrange.grid, but this requires "manually" aligning the plots if there are different length labels etc. Additionally, I would like to have the facet labels included in the plot which is not an available option with the arrange.grid solution. Also I haven't tried viewports yet. Maybe that is the solution, but I was hoping for more of the faceted look to this plot and that seems to be more similar to grid.arrange.</p>
  
  <p>It seems to me as though this is a bug, but I am open to an explanation as to how this might be a "feature". I also hope that there might be a simple solution to this problem that I have not thought of yet!</p>