title: How to process a date diference using same id elements in a list
body: <p><strong>I have the following data structure:</strong></p>
  
  <pre><code>[ (19L, datetime.datetime(2015, 2, 11, 12, 3, 43)),
    (19L, datetime.datetime(2015, 2, 12, 16, 28, 48)),
    (19L, datetime.datetime(2014, 9, 17, 11, 58, 19)),
    (80L, datetime.datetime(2014, 9, 15, 12, 54, 36)),
    (80L, datetime.datetime(2014, 9, 15, 14, 16, 39)),
    (80L, datetime.datetime(2014, 2, 6, 8, 58, 39)),
    (80L, datetime.datetime(2014, 9, 8, 14, 21, 48)),
    (90L, datetime.datetime(2016, 8, 2, 18, 14, 31)),
    (90L, datetime.datetime(2016, 8, 2, 21, 14, 23)),
    (90L, datetime.datetime(2014, 1, 5, 16, 35, 34))  ]
  </code></pre>
  
  <p>And i need to calculate the average days between the days from users with same id, first element corresponds to user id's and the second one to a datetime.</p>
  
  <p>I'm getting trouble on how to iterate through the list, counting and getting the same diff for each user...</p>