title: How do I match two arrays with duplicates in Ruby?
body: <p>I know this removes duplicates :</p>
  
  <pre><code>@email.distributions.map(&amp;:zip_code) &amp; CardSignup.all.map(&amp;:zip_code)
  </code></pre>
  
  <p>But I want to do the same thing, where I find anything that matches, but it also shows me duplicates.</p>
  
  <p>Any ideas?</p>
  
  <p>I am trying to find the amount of people who signed up for a card that have a matching zip code to a zip code preference I placed.</p>