title: ggplot to stack bar graph top 5 for each month
body: <p>I have a good one. I've thinking about this a long time now. I have this data set and this data set could be be huge. I would like to graph a ggplot stack bar based on top 5 higest count for each month. For example, for 1//1/2012, the higest counts would be I, G, F, D and E.</p>
  
  <p>df</p>
  
  <pre><code>Date    Desc    count
  1/1/2012    A   10
  1/1/2012    B   5
  1/1/2012    C   7
  1/1/2012    D   25
  1/1/2012    E   19
  1/1/2012    F   30
  1/1/2012    G   50
  1/1/2012    H   10
  1/1/2012    I   100
  2/1/2012    A   10
  2/1/2012    B   5
  2/1/2012    C   7
  2/1/2012    D   25
  2/1/2012    E   19
  2/1/2012    F   30
  2/1/2012    G   50
  2/1/2012    H   10
  2/1/2012    I   100
  3/1/2012    A   1
  3/1/2012    B   4
  3/1/2012    C   5
  3/1/2012    D   6
  3/1/2012    E   6
  3/1/2012    F   7
  3/1/2012    G   8
  3/1/2012    H   5
  3/1/2012    I   10
  </code></pre>
  
  <p>I have something like this but this graphs all of the values:</p>
  
  <pre><code> ggplot(df, aes(Date, count))+ geom_bar(aes(fill=Desc), stat="identity", position="stack") + theme_bw()
  </code></pre>