title: Overlaying geom_point layer on a geom_boxplot
body: <p>Really struggling with this. </p>
  
  <p><code>a</code> &amp; <code>b</code> are actual datasets in the real world, <code>a</code> being extremely large. I get an error ggplot2 doesn't know how to deal with data of class uneval. What I'm trying to do is overlay a single point from a second data set on to the boxplot to highlight how one particular sample compared to a universe.</p>
  
  <p>Any idea what I'm doing wrong? How can I fix it?</p>
  
  <pre><code>a = data.frame(YTD.Retn=runif(1000,-10,10),sector="a")
  a = rbind(a,data.frame(YTD.Retn=runif(1000,-10,10),sector="b"))
  a = rbind(a,data.frame(YTD.Retn=runif(1000,-10,10),sector="c"))
  a = rbind(a,data.frame(YTD.Retn=runif(1000,-10,10),sector="d"))
  a = rbind(a,data.frame(YTD.Retn=runif(1000,-10,10),sector="e"))
  a = rbind(a,data.frame(YTD.Retn=runif(1000,-10,10),sector="f"))
  a = rbind(a,data.frame(YTD.Retn=runif(1000,-10,10),sector="g"))
  
  b = data.frame(sector=c("a","b","c","d","e","f","g"),YTD.Retn=c(5,6,7,3,2,-1,-5))
  
  p1 =ggplot(a,aes(factor(sector),YTD.Retn,fill=factor(sector))) + geom_boxplot() +
    scale_fill_discrete(guide=F) +
    geom_point(b,aes(factor(sector),YTD.Retn))
  
  plot(p1)
  </code></pre>