title: ggplot2 v2.21.9 sec.axis in polar plot
body: <p>I am currently trying to add a secondary axis using the recently introduced function <code>sec.axis</code> in <code>ggplot2</code>. This function works well with scatter/bar plots, but not for polar plot: In the following code, the name for the second y-axis appears, but not the axis.</p>
  
  <p>Is there any workaround or option, that I have not figured out?</p>
  
  <pre><code>require(ggplot2)
  set.seed(40);
  Location &lt;- data.frame(Winkel = round(runif(1000, 0, 24), 0))
  Location$BAD &lt;- Location$Winkel %in% c(seq(7, 18))
  Abschnitte &lt;- c(0:24)
  
  polar &lt;- data.frame(Winkel2 = c(1.5, 2.34, 1.2, 3.45, 1.67, 2.61, 1.11, 13.2), 
                      value = c(0.1, 0.03, 0.02, 0.015, 0.01, 0.04, 0.09, 0.06))
  
  ggplot(Location, aes(x = Winkel, fill = BAD, y = (..count..)/sum(..count..))) + 
    geom_histogram(breaks = seq(0,24), colour = "black") + 
    coord_polar(start = 0) + theme_minimal() +
    scale_fill_brewer(type = "seq", palette = 3) +
    ylab("Percentual allocation time") + 
    ggtitle("") +
    scale_x_continuous("", limits = c(0, 24), breaks = Abschnitte, labels = Abschnitte) +
    scale_y_continuous(labels = scales::percent,
             sec.axis = sec_axis(~.*5, name = "mean direction")) +
    geom_segment(data = polar, aes(x = Winkel2, y = 0, xend = Winkel2, yend = value, fill = NA), 
                 arrow = arrow(angle = 30, type = "closed", length = unit(0.3, "cm")))
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/cPFy9.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/cPFy9.jpg" alt="enter image description here"></a></p>