title: Get unique array values using mask
body: <p>I have an array of URLs and corresponding domains<br>
  Delimiter for array values is <code>\n</code><br>
  Domain/Url delimiter is comma</p>
  
  <pre><code>site1.com,www.site1.com/blahA-blahB-blahC   
  site2.com,site2.com/blahD-blahE-blahF   
  site2.com,site2.com/blahG-blahH-blahI   
  site3.com,site3.com/blahJ-blahK-blahL
  </code></pre>
  
  <p>I would like to filter this array and remove lines that contain domain duplicates (1st occurrence stays). Required output is as follows:</p>
  
  <pre><code>site1.com,www.site1.com/blahA-blahB-blahC   
  site2.com,site2.com/blahD-blahE-blahF   
  site3.com,site3.com/blahJ-blahK-blahL
  </code></pre>
  
  <p>Please, advise. </p>