title: Check array for duplicates, return only items which appear more than once
body: <p>I have an text document of emails such as</p>
  
  <pre><code>Google12@gmail.com,
  MyUSERNAME@me.com,
  ME@you.com,
  ratonabat@co.co,
  iamcool@asd.com,
  ratonabat@co.co,
  </code></pre>
  
  <p>I need to check said document for duplicates and create a unique array from that (so if "ratonabat@co.co" appears 500 times in the new array he'll only appear once.)</p>
  
  <p>Edit:
  For an example:</p>
  
  <pre><code>username1@hotmail.com
  username2@hotmail.com
  username1@hotmail.com
  username1@hotmail.com
  username1@hotmail.com
  username1@hotmail.com
  </code></pre>
  
  <p>This is my "data" (either in an array or text document, I can handle that)</p>
  
  <p>I want to be able to see if there's a duplicate in that, and move the duplicate ONCE to another array. So the output would be</p>
  
  <pre><code>username1@hotmail.com
  </code></pre>