title: removing all the space between two ggplots combined with grid.arrange
body: <p>I want to stick two plots without any space between theme (so they share one axis).</p>
  
  <p>Given:</p>
  
  <pre><code>p1 &lt;- qplot(1,1,xlab="")
  
  p1 &lt;- p1 +
    theme(legend.position="none",
          axis.text.x=element_blank(),
          axis.ticks.x=element_blank(),
          plot.margin=unit(c(1,1,0,1), "cm"),
          panel.margin=unit(c(1,1,0,1), "cm"))
  p2 &lt;- qplot(1,2)
  
  grid.arrange(p1,p2)
  </code></pre>
  
  <p>Which produces:</p>
  
  <p><img src="https://i.stack.imgur.com/qC4ux.jpg" alt="enter image description here"></p>
  
  <p>I want to eliminate the white space between the two plots.</p>
  
  <p>I have the impression tweaking heights, as has been done for widths in : <a href="https://stackoverflow.com/questions/13294952/left-align-two-graph-edges-ggplot/13295880#13295880">left align two graph edges (ggplot)</a> is the solution, but can't figure it out.</p>