title: grid.arrange ggplot2 plots by columns instead of by row using lists
body: <p>I want create a multiplot of <code>ggplot2</code> plots from a list using <code>grid.arrange</code> but arrange them by columns before doing it by rows.</p>
  
  <pre><code>gg_list1 &lt;- list(qplot(mpg, disp, data = mtcars), 
                   qplot(hp, wt, data = mtcars), 
                   qplot(qsec, wt, data = mtcars))
  
  gg_list2 &lt;- list(qplot(mpg, disp, data = mtcars), 
                   qplot(hp, wt, data = mtcars), 
                   qplot(qsec, wt, data = mtcars))
  </code></pre>
  
  <p>I know I can do this:</p>
  
  <pre><code>do.call(grid.arrange,c(gg_list1,gg_list2 , ncol = 2, nrow  = 3))
  </code></pre>
  
  <p>but it fills from left to right before top to bottom.</p>
  
  <p>I've tried this:</p>
  
  <pre><code> do.call(grid.arrange, c(gg_list1, arrangeGrob(gg_list2, nrow = 3), ncol = 2))
  </code></pre>
  
  <p>But get <code>Error: length(widths) == ncol is not TRUE</code></p>
  
  <p>Any ideas?</p>