title: Setting width and height of a single panel in multi-panel plot in cowplot::plot_grid
body: <p>I am making a multi-panel plot using <code>ggplot2</code> and <code>cowplot</code> packages, but I need to change the height of a single plot. It is easiest shown with an example</p>
  
  <pre><code>library(ggplot2)
  library(cowplot)
  
  p1 &lt;- ggplot(iris, aes(Sepal.Width, Sepal.Length, colour = Species)) + 
               geom_point() +
               theme(axis.text.x = element_blank(),
                     axis.title.x = element_blank(),
                     legend.position = "none")
  p2 &lt;- ggplot(iris, aes(Sepal.Width, Sepal.Length, colour = Species)) + 
               geom_point() +
               theme(axis.text.x = element_blank(),
                     axis.title.x = element_blank(),
                     axis.text.y = element_blank(),
                     axis.title.y = element_blank(),
                     legend.position = "none")
  p3 &lt;- ggplot(iris, aes(Sepal.Width, Sepal.Length, colour = Species)) + 
               geom_point() +
               theme(axis.text.y = element_blank(),
                     axis.title.y = element_blank(),
                     legend.position = "none")
  p4 &lt;- ggplot(iris, aes(Sepal.Width, Sepal.Length, colour = Species)) + 
               geom_point() + 
               theme(legend.position = "none")
  p5 &lt;- ggplot(iris, aes(Sepal.Width, Sepal.Length, colour = Species)) + 
               geom_point() +
               theme(axis.text.y = element_blank(),
                     axis.title.y = element_blank(),
                     legend.position = "none")
  
  pL &lt;- ggplot(iris, aes(Sepal.Width, Sepal.Length, colour = Species)) + geom_point()
  l &lt;- get_legend(pL)
  
  # simple grid
  plot_grid(p1, p2, p3, p4, p5, l, ncol = 3)
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/9AtFS.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/9AtFS.png" alt="enter image description here"></a></p>
  
  <p>As you can see the y axis in the far right top panel has been shrunk in comparison with the two other panels in the same row by the inclusion of the x-axis title. </p>
  
  <p>So <strong>how do I set the relative height and width of this single panel, so that the y-axis aligns with the y-axis of the panels in the top row?</strong></p>
  
  <p>You cannot set individual panels using <code>rel_heights =</code> and <code>rel_widths() =</code> arguments, and when I tried to add <code>axis = "tblr"</code> and <code>align = "hv"</code> arguments I got the error message </p>
  
  <pre><code>Error in `[.unit.list`(sizes[[x]], list_indices[[x]]) : 
    index out of bounds (unit list subsetting) 
  </code></pre>