title: Trying to figure out days between every event based on user id in excel
body: <p>Trying to figure out the number of days for every user's play event with respect to its first event . i.e (t1-f), (t2-f) etc. for every user id</p>
  
  <p>Input </p>
  
  <pre><code>     date        id     event   changepoint of user id
      1/25/2019   10002   Play    f
      1/25/2019   10002   Play    t
      1/1/2019    10004   Play    f
      1/30/2019   10012   Play    f
      1/30/2019   10012   Play    t
      2/13/2019   10012   Play    t
      1/19/2019   10013   Play    f
      1/19/2019   10013   Play    t
      1/19/2019   10013   Play    t
      1/21/2019   10013   Play    t
      2/3/2019    10019   Play    f
      2/3/2019    10019   Play    t
  </code></pre>
  
  <p>With the formula that i am using , i am just getting difference of days between current and previous day.</p>
  
  <p>Expected output</p>
  
  <pre><code>date         id     event   cp  days
  1/25/2019   10002   Play    f   0
  1/25/2019   10002   Play    t   0  (t-f)
  1/1/2019    10004   Play    f   0
  1/30/2019   10012   Play    f   0
  1/30/2019   10012   Play    t   0  (t-f)
  2/13/2019   10012   Play    t   14 (t-f)
  1/19/2019   10013   Play    f   0
  1/19/2019   10013   Play    t   0  (t-f)
  1/19/2019   10013   Play    t   0  (t-f)
  1/21/2019   10013   Play    t   2  (t-f)
  2/3/2019    10019   Play    f   0  (t-f)
  2/3/2019    10019   Play    t   0  (t-f)
  </code></pre>