title: Shared legend in subplots
body: <p>I'm trying to translate some of my R code to Julia. I mainly struggle with the difference in plotting as I'm very used to ggplot2.</p>
  <p>There I can do:</p>
  <pre><code>mpg %&gt;% 
  ggplot(aes(x = displ, y = cyl, color = manufacturer)) + 
  geom_point() + 
  facet_wrap(~class)
  </code></pre>
  <p>With this I get subplots, consistent x- and y-axes, a shared legend, and much more.
  How would I achieve this with Julia, say the GR backend?</p>
  <p>Update: The <code>mpg</code> data set looks like:</p>
  <pre><code># A tibble: 234 × 11
     manufacturer model      displ  year   cyl trans      drv     cty   hwy fl    class  
     &lt;chr&gt;        &lt;chr&gt;      &lt;dbl&gt; &lt;int&gt; &lt;int&gt; &lt;chr&gt;      &lt;chr&gt; &lt;int&gt; &lt;int&gt; &lt;chr&gt; &lt;chr&gt;  
   1 audi         a4           1.8  1999     4 auto(l5)   f        18    29 p     compact
   2 audi         a4           1.8  1999     4 manual(m5) f        21    29 p     compact
   3 audi         a4           2    2008     4 manual(m6) f        20    31 p     compact
   4 audi         a4           2    2008     4 auto(av)   f        21    30 p     compact
   5 audi         a4           2.8  1999     6 auto(l5)   f        16    26 p     compact
   6 audi         a4           2.8  1999     6 manual(m5) f        18    26 p     compact
   7 audi         a4           3.1  2008     6 auto(av)   f        18    27 p     compact
   8 audi         a4 quattro   1.8  1999     4 manual(m5) 4        18    26 p     compact
   9 audi         a4 quattro   1.8  1999     4 auto(l5)   4        16    25 p     compact
  10 audi         a4 quattro   2    2008     4 manual(m6) 4        20    28 p     compact
  # … with 224 more rows
  </code></pre>
  <p>and the output I'm after would look something like:
  <a href="https://i.stack.imgur.com/9k4YA.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/9k4YA.png" alt="R plot" /></a></p>