title: Filtering logic with timedelta in panel data
body: <p>For each id <code>id</code>, i want to apply the following logic of filtering:</p>
  
  <p>First identify which is the oldest time for each id.
  Second if the following rows had a time difference of less than 5 minutes from the oldest time, drop it.
  Once 5 minutes pass from the oldest time for each id, find the following oldest time and repeat again the rule if the following rows had a time difference of less than 5 minutes from this new oldest time, drop them</p>
  
  <pre><code>df
                 time  track  id
  2018-07-06 08:34:44       1   1
  2018-07-06 08:35:46       1   1
  2018-07-19 09:15:50       1   1
  2018-07-19 09:17:23       1   1
  2018-07-06 07:34:44       1   2
  2018-07-06 07:36:46       1   2
  2018-07-06 07:37:50       1   2
  2018-07-06 07:37:53       1   2
  </code></pre>
  
  <p>Expected result</p>
  
  <pre><code>               time  track  id
  2018-07-06 08:34:44       1   1
  2018-07-19 09:15:50       1   1
  2018-07-06 07:34:44       1   2
  </code></pre>