title: average column values across all rows of a data frame
body: <p>I've got a data frame that I read from a file like this:</p>
  
  <pre><code>name, points, wins, losses, margin
  joe, 1, 1, 0, 1
  bill, 2, 3, 0, 4
  joe, 5, 2, 5, -2
  cindy, 10, 2, 3, -2.5
  </code></pre>
  
  <p>etc.</p>
  
  <p>I want to average out the column values across all rows of this data, is there an easy way to do this in R?</p>
  
  <p>For example, I want to get the average column values for all "Joe's", coming out with something like</p>
  
  <pre><code>joe, 3, 1.5, 2.5, -.5
  </code></pre>