title: Group and gave ranks based on certain conditions
body: <p>I want to give rank to below data based on time (if the timestamp difference is less the 15 mins then same rank else rank +1 )
  E.g </p>
  
  <ul>
  <li>time : 06:10:32 and 06:12:38 should get rank 1</li>
  <li>time : 13:36:44 and 13:40:41 and 13:44:47 should get rank 2</li>
  <li>and last 4 rows should get rank 3</li>
  </ul>
  
     
  
  <pre><code>user_id ride_id      createdat_local    
  2681233 96783742    2017-10-04 06:10:32 
  2681233 96784171    2017-10-04 06:12:38 
  2681233 96924751    2017-10-04 13:36:44 
  2681233 96925561    2017-10-04 13:40:41 
  2681233 96926560    2017-10-04 13:44:47 
  2681233 96994651    2017-10-04 18:12:29 
  2681233 96995953    2017-10-04 18:18:16 
  2681233 96996937    2017-10-04 18:22:15 
  2681233 96997195    2017-10-04 18:24:00 
  </code></pre>