title: ggplot2 change axis limits for each individual facet panel
body: <pre class="lang-r prettyprint-override"><code>library(tidyverse)
  ggplot(mpg, aes(displ, cty)) + 
    geom_point() + 
    facet_grid(rows = vars(drv), scales = "free")
  </code></pre>
  
  <p><img src="https://i.imgur.com/Pg1Yoou.png" alt=""></p>
  
  <p>The ggplot code above consists of three panels <code>4</code>, <code>f</code>, and <code>r</code>. I'd like the y-axis limits to be the following for each panel:</p>
  
  <pre class="lang-r prettyprint-override"><code>Panel y-min y-max breaks
  ----- ----- ----- ------
  4     5     25    5
  f     0     40    10
  r     10    20    2
  </code></pre>
  
  <p>How do I modify my code to accomplish this? Not sure if <code>scale_y_continuous</code> makes more sense or <code>coord_cartesian</code>, or some combination of the two.</p>