title: Gremlin : GroupBy vertices , having count > 1
body: <p>I am using TITAN 0.4, and gremlin for traversals.
  My requirement is to identify duplicate vertices in graph, and to merge those.
  There are > 15 M vertices in graph.</p>
  
  <pre><code>gremlin&gt; g.V.has('domain').groupBy{it.domain}{it.id}.cap
  
  ==&gt;{google.com=[4], yahoo.com=[16, 24, 20]}
  </code></pre>
  
  <p>I am able to group the vertices, but I need only those domains(vertices) which exists more than once. </p>
  
  <p>In the above example, I need to return only <code>==&gt;{yahoo.com=[16, 24, 20]}</code>
  The key "domain" is indexed, if that makes any difference.</p>
  
  <p>Please help me here</p>