title: Combine geom_boxplot with geom_line
body: <p>I would like to combine a boxplot and a line plot using <code>ggplot2</code>. However, I am struggling to have lines for each group (<code>g</code>) connecting points across the categories on the x-axis.</p>
  <p>To demonstrate the problem:</p>
  <pre><code>df &lt;- data.frame(x = rep(letters[1:3],each=5), 
                   y = c(1:5,sample(10,5),1:5), 
                   g = rep(LETTERS[1:5],3) )
  
  library(ggplot2)
  ggplot(df, aes(x=x,y=y)) + geom_boxplot() + geom_point(aes(colour = g))
  </code></pre>
  <p><img src="https://i.stack.imgur.com/A9XOW.jpg" alt="enter image description here" /></p>
  <p>I want to have a line connecting all <code>A</code> points, a line connecting all <code>B</code> points and so on.</p>
  <p>I have looked at some answers here but I cannot incorporate them. They suggest using <code>group=1</code> but this will not suit my individual lines for each group in <code>g</code>. Is it possible using <code>stat_summary</code> maybe?</p>