title: 'Labels on top' with facet_grid, or 'space option' with facet_wrap
body: <p><code>facet_grid</code> allow me to size each facet width according to number of items on y axis (<code>space</code> argument):</p>
  
  <pre><code>df &lt;- data.frame(label = c("Variable one", rep("Variable two", 2), rep("Variable three", 3)), item = c("A", "B", "C", "D", "E", "F"), value = rnorm(6))
  ggplot(df, aes(x = value, y = item)) + 
  geom_point() + 
  facet_grid(label ~ ., scales = "free_y", space = "free_y") + 
  ylab("") + 
  theme(strip.text.y = element_text(angle=0))
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/c82RZ.png" alt="enter image description here"></p>
  
  <p>But I would like facet labels on top, so I switch to <code>facet_wrap</code>, and lost the <code>space</code> argument (facets have all the same width):</p>
  
  <pre><code>ggplot(df, aes(x = value, y = item)) + 
  geom_point() + 
  facet_wrap(~ label, scales = "free_y", ncol = 1) + 
  ylab("")
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/H4O89.png" alt="enter image description here"></p>
  
  <p>Is it possible to obtain the best of both worlds? </p>
  
  <p>Thank you in advance for your help.</p>