My data set looks like below
ID     Diagnosis date    Procedure date
1      2005-09-09        2008-04-09
1      2006-05-09        2007-08-08
2      2007-07-02        2007-08-01
2      2007-07-02        2009-08-05
2      2008-05-8         2007-08-10
I want to group my data like below
ID      Diagnosis date     Procedure date
1       2005-09-09         2007-08-08
        2006-05-09         2008-04-09
2       2007-07-02         2007-08-01
                           2007-07-10
        2008-05-08         2009-08-05
Basically the procedure date should be after the diagnosis date
 
     
    