title: calculate different between consecutive date records at an ID level
body: <p>I have a dataframe as</p>
  <pre><code>   col 1     col 2
      A         2020-07-13 
      A         2020-07-15 
      A         2020-07-18 
      A         2020-07-19
      B         2020-07-13
      B         2020-07-19 
      C         2020-07-13
      C         2020-07-18 
     
  </code></pre>
  <p>I want it to become the following in a new dataframe</p>
  <pre><code>    col_3     diff_btw_1st_2nd_date   diff_btw_2nd_3rd_date  diff_btw_3rd_4th_date
       A              2                       3                       1
       B              6                       NaN                     NaN
       C              5                       NaN                     NaN
  </code></pre>
  <p>I tried getting the groupby at Col 1 level , but not getting the intended result. Can anyone help?</p>