title: Add secondary X axis labels to ggplot with one X axis
body: <p>**Edit, there are two great solutions here, one is marked as the answer, but @hrbrmstr provides a great solution combining two ggplots which works well for this simple plot.* </p>
  
  <p>Here's the code</p>
  
  <pre><code>breaks.major &lt;- c(0,15,37.5,52.5,67.5,82.5,95,100) #defines the midpoints of the categories (label locations)
  breaks.minor &lt;- c(30,45,60,75,90) #defines the edges of the categories (second label set I need)
  labels.minor &lt;- c("","Extremely \nDissatisfied","Dissatisfied","Uncertain","Satisfied","Very \nSatisfied","Extremely \nSatisfied","")
  lims =c(0,100)
  g &lt;- ggplot(mpg, aes(class))+
    geom_bar()+
    coord_flip()+
    scale_y_continuous(limit = lims, minor_breaks = breaks.minor, breaks = breaks.major, labels = labels.minor) +
    theme(panel.grid.major.x = element_blank()) +
    theme(panel.grid.major.y = element_blank()) +
    theme(axis.ticks.x=element_blank()) +
    theme(axis.title= element_blank()) 
  </code></pre>
  
  <p>It produces this plot:</p>
  
  <p><a href="https://i.stack.imgur.com/dOBCw.png" rel="noreferrer"><img src="https://i.stack.imgur.com/dOBCw.png" alt="enter image description here"></a></p>
  
  <p>I need to have two sets of X-axis labels, one showing the category names (i.e. the "satisfied" etc. that are already there via <code>labels.minor</code>), and one showing the values at the <code>breaks.minor</code> locations (corresponding to the category limits, i.e. the vertical panel grid lines). I need the current <code>labels.minor</code> labels to be below the required additional labels.</p>
  
  <p>I currently do this with line breaks so that the numbers and categories are all in one long string, but the spacing gets funny with plot resizes.I could do this with text boxes (I assume), is there a way within ggplot? </p>
  
  <p>Extra points if you get my current labels in the centre of their sections (e.g. "Extremely Satisfied" is off-centre)</p>
  
  <p>This is my desired output (pardon my 'mspaint')</p>
  
  <p><a href="https://i.stack.imgur.com/9jVfl.png" rel="noreferrer"><img src="https://i.stack.imgur.com/9jVfl.png" alt="enter image description here"></a></p>