title: Getting rid of commonalities in array
body: <p>I have these arrays:</p>
  
  <pre><code>x = ['a','b','c','d']
  y = ['b','c','e']
  </code></pre>
  
  <p>I'd like to get rid of the commonalities in <code>x</code> and <code>y</code> and ignore the non-commonalities in <code>y</code>.</p>
  
  <p>Ideally, when I do something to the two arrays, I would get <code>['a','d']</code>.</p>
  
  <p>Is there something that does this in Ruby?</p>