title: Using Cowplot for a list of plots using paste0
body: <p>I have a list of ggplots from 1:10 called <code>plot_1</code>,<code>plot_2</code>....<code>plot_10</code>.</p>
  
  <p>I wanted to use cowplot to display all plots together.</p>
  
  <p>How can I use <code>plot.grid()</code> to call all plots? i.e I want to write something like</p>
  
  <pre><code>plot.grid(paste0("plot",1:10)) 
  </code></pre>
  
  <p>but this doesn't work - I get the error:</p>
  
  <blockquote>
    <p>Error in ggplot_to_gtable(x) : 
      Argument needs to be of class "ggplot" or "gtable"*</p>
  </blockquote>