title: Merging multiple documents in mongodb
body: <p>I have here a collection of two documents in a mongodb database (I am using robomongo)<img src="https://i.stack.imgur.com/5VCz5.png" alt="list of documents in my collection"></p>
  
  <p>I took the solution from
  <a href="https://stackoverflow.com/questions/27020038/how-can-i-merge-many-documents-into-a-single-document-and-move-to-another-collec">How can I merge many documents into a single document and move to another collection?</a></p>
  
  <p>However I am ending up empty</p>
  
  <p><img src="https://i.stack.imgur.com/EOaTP.png" alt="error"></p>
  
  <p>The code of the original documents are as follows:</p>
  
  <pre><code>{
  "_id" : ObjectId("5534e79726092822df7528ff"),
  "labels" : {
      "urls" : "http://planet-e.nethttp://planetecommunications.bandcamp.comhttp://www.discogs.com/user/planetedetroithttp://www.facebook.com/planetedetroithttp://www.flickr.com/photos/planetedetroithttp://plus.google.com/100841702106447505236http://myspace.com/planetecomhttp://myspace.com/planetedetroithttp://soundcloud.com/planetedetroithttp://twitter.com/planetedetroithttp://vimeo.com/user1265384http://www.youtube.com/user/planetedetroithttp://en.wikipedia.org/wiki/Planet_E_Communications",
      "id" : "1",
      "name" : "Planet E",
      "sublabels" : "Antidote (4)Community ProjectsGuilty PleasuresI Ner Zon SoundsPlanet E Communications, Inc.TWPENTY",
      "contactinfo" : "Planet E Communications\nP.O. Box 27218\nDetroit, 48227, USA\n\np: 313.874.8729 \nf: 313.874.8732\n\nemail: info AT Planet-e DOT net\n",
      "profile" : "Classic Techno label from Detroit, USA.\n[b]Label owner:[/b] [a=Carl Craig].\n",
      "dataquality" : "Needs Vote"
  }
  }
  
  
   {
  "_id" : ObjectId("5534e79726092822df752900"),
  "labels" : {
      "id" : "2",
      "name" : "Earthtones Recordings",
      "sublabels" : [],
      "contactinfo" : "Seasons Recordings\n2236 Pacific Avenue\nSuite D\nCosta Mesa, CA  92627\n\ntel: +1.949.574.5255\nfax: +1.949.574.0255\n\nemail: &lt;a href=\"mailto:jthinnes@seasonsrecordings.com\"&gt;jthinnes@seasonsrecordings.com&lt;/a&gt;\n",
      "profile" : "California deep house label founded by Jamie Thinnes. Now defunct and continued as [l=Seasons Recordings].",
      "dataquality" : "Correct",
      "urls" : "http://www.seasonsrecordings.com/"
  }
  }
  </code></pre>
  
  <p>I want to combine both the documents as one document under one title "label"</p>