title: plot geom_point on top of boxplot from different data set
body: <p>I have a dataset <code>a</code> from which I make a set of boxplots. On top of these boxplots I want to plot a <code>geom_point</code> which is just a subset of the original data set. The subset is stored in <code>b</code>.</p>
  
  <p>What I am doing wrong to get this error?</p>
  
  <pre><code>ggplot(a, aes(x=reorder(miRNA,as.numeric(value)),y=as.numeric(value))) + geom_boxplot() +
    geom_point(b, aes(x=reorder(miRNA,as.numeric(value)))) +
    theme(axis.text.x = element_text( angle = 90)) +
    coord_flip() +
    scale_y_continuous(limits=c(-5, 5)) +
    theme_bw(base_size = 8) +
    labs(x = "miRNA", y = "log2 tumor/benign") 
  </code></pre>
  
  <blockquote>
    <p>Error: ggplot2 doesn't know how to deal with data of class uneval</p>
  </blockquote>
  
  <pre><code>&gt; head(a)
               miRNA variable      value
  2    hsa-let-7b-5p   ta.008 -0.1512121
  3    hsa-let-7c-5p   ta.008 -0.2649810
  11  hsa-miR-10a-5p   ta.008 -1.6736331
  13  hsa-miR-122-5p   ta.008  0.0417420
  15 hsa-miR-125a-5p   ta.008 -0.8262042
  19  hsa-miR-128-3p   ta.008 -0.2867184
  &gt; head(b)
                 miRNA variable     value
  2670   hsa-let-7b-5p   tb1302  1.313482
  2671   hsa-let-7c-5p   tb1302  1.071200
  2679  hsa-miR-10a-5p   tb1302  1.728654
  2681  hsa-miR-122-5p   tb1302  1.013428
  2683 hsa-miR-125a-5p   tb1302 -0.274418
  2687  hsa-miR-128-3p   tb1302 -4.967844
  </code></pre>