title: grouped bar graph
body: <p>I have the following data:</p>
  
  <pre><code>bin groupname   total_dist
  0   rowA    377
  0   rowA    306.6
  0   rowB    2.1
  0   rowB    110.6
  1   rowA    918.1
  1   rowA    463.2
  1   rowB    798.2
  1   rowB    1196
  2   rowA    1295.1
  2   rowA    1269.1
  2   rowB    698
  2   rowB    1022.1
  </code></pre>
  
  <p>Using R, I want to make a bar graph where there is a bar for rowA and a bar for rowB for <em>each</em> bin.  I can group total_dist by one or the other (<code>plot(total_dist~bin)</code> or <code>plot(total_dist~groupname)</code>). But I can't figure out how to combine them.</p>
  
  <p>I want something that looks similar to this example:
  <img src="https://upload.wikimedia.org/wikipedia/en/timeline/e6dba37eba64dc9b0341bdffc002343d.png" alt="example grouped bar graph"></p>