title: Mongo Aggregation remove all records for a id and only keeping the oldest one
body: <p>have a collection with values</p>
  
  <pre><code>_id:ObjectId('......')
  ton_id :ObjectId('abcd')
  value:587900
  date:2019-12-13T07:09:40.075+00:00
  
  
  _id:ObjectId('......')
  ton_id :ObjectId('abcd')
  value:50540
  date:2018-1-13T07:09:40.075+00:00
  
  _id:ObjectId('......')
  ton_id :ObjectId('abcd1')
  value:55400
  date:2019-5-13T07:09:40.075+00:00
  
  
  _id:ObjectId('......')
  ton_id :ObjectId('abcd1')
  value:22500
  date:2018-12-13T07:09:40.075+00:00
  
  
  </code></pre>
  
  <p>for the ton_ids <code>abcd</code> and <code>abcd1</code> remove all the records except the oldest one.</p>
  
  <p>required output</p>
  
  <pre><code>_id:ObjectId('......')
  ton_id :ObjectId('abcd')
  value:50540
  date:2018-1-13T07:09:40.075+00:00
  
  
  
  _id:ObjectId('......')
  ton_id :ObjectId('abcd1')
  value:22500
  date:2018-12-13T07:09:40.075+00:00
  
  </code></pre>