title: ggplot2: Reversing secondary continuous x axis
body: <p>I am trying to reverse the secondary X axis on top of my ggplot. </p>
  
  <pre><code>ggplot(
    data=MasterTable, aes(x=Concentration, y=Signal, color=factor(Assay))) + 
    scale_x_continuous("Chemical 1", 
                       sec.axis = sec_axis(~ . *1, name = "Chemical 2"), scale_x_reverse(limits=c(400,0)))
  </code></pre>
  
  <p>If you remove the last section of the code (<code>scale_x_reverse</code>...) it makes a plot with a secondary that is identical to the bottom X axis. I have managed to reverse the bottom axis but this also reverses the top axis. I am looking to only reverse the top axis. </p>
  
  <p>Any help on this would be really appreciated.</p>
  
  <p>Thanks!</p>
  
  <p><a href="https://i.stack.imgur.com/aUd4S.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/aUd4S.jpg" alt="enter image description here"></a></p>