title: ggplot2 - Overlay Mean of Each Group
body: <p>I am trying to mimic this lattice plot using ggplot.  The data for this plot is <code>lme4::Dyestuff</code>.  </p>
  
  <p><img src="https://i.stack.imgur.com/SyBUj.png" alt="enter image description here"></p>
  
  <p>I am able to plot each of the points in a similar manner, but I am unable to plot the line which represents the mean of each batch.</p>
  
  <pre><code>library (lme4)
  library (ggplot2)
  
  ggplot (Dyestuff, aes (Yield, Batch, colour = Batch)) + geom_jitter ()
  </code></pre>
  
  <p>Q. How can I add this line using ggplot?  Notice also how the batches on the y-axis are ordered by the mean yield of the batch.</p>