title: How to move or position a legend in ggplot2
body: <p>I'm trying to create a ggplot2 plot with the legend beneath the plot.</p>
  
  <p>The ggplot2 book says on p 112 "The position and justification of legends are controlled by the theme setting legend.position, and the value can be right, left, top, bottom, none (no legend), or a numeric position". </p>
  
  <p>The following code works (since "right" it is the default), and it also works with "none" as the legend position, but "left", "top", "bottom", all fail with "Error in grid.Call.graphics("L_setviewport", pvp, TRUE) :  Non-finite location and/or size for viewport"</p>
  
  <pre><code>library(ggplot2)
  (myDat &lt;- data.frame(cbind(VarX=10:1, VarY=runif(10)), 
      Descrip=sample(LETTERS[1:3], 10, replace=TRUE)))
  qplot(VarX,VarY, data=myDat, shape=Descrip) + 
      opts(legend.position="right")
  </code></pre>
  
  <p>What am I doing wrong? Re-positioning a legend must be incredibly common, so I figure it's me.</p>