Finding the difference between dates in subsequent rows

[advmsj]

Happy weekend, I am trying to find the time to readmission (last column). I ordered my data by ID and I wish to find the time from the previous hospital discharge to the next readmission. For example. for ID 1, I would like to know the time between 01/30/17 and 03/27/19, and 04/10/19 and 07/02/20. I am unsure of how to do this in SAS. Any help is appreciated

ID	BirthDate	Admit Date	Discharge Date	Times ill	Time to readmission
1	12/07/95	01/01/17	01/30/17	1
1	12/07/95	03/27/19	04/10/19	2
1	12/07/95	07/02/20	07/25/20	3
2	12/24/99	03/13/16	03/27/16	1
2	12/24/99	10/20/19	11/03/19	2
3	07/26/98	05/10/17	05/30/17	1
4	09/29/82	06/30/18		1

[PaigeMiller]

UNTESTED CODE (If you want tested code, please provide the data as a SAS data step)

data want;
    set have;
    by id;
    prev_discharge=lag(discharge_date);
    if not first.id then time_to_readmission=admit_date-prev_discharge;
    else time_to_readmission=.;
    drop prev_discharge;
run;
 

[novinosrin · Accepted solution]

data have;
input ID	(BirthDate	Admitdate	DischargeDate) (:mmddyy10.)	Timesill;
format BirthDate	Admitdate	DischargeDate mmddyy10.;
cards;
1	12/7/1995	1/1/2017	1/30/2017	1
1	12/7/1995	3/27/2019	4/10/2019	2
1	12/7/1995	7/2/2020	7/25/2020	3
2	12/24/1999	3/13/2016	3/27/2016	1
2	12/24/1999	10/20/2019	11/3/2019	2
3	7/26/1998	5/10/2017	5/30/2017	1
4	9/29/1982	6/30/2018		.	1
;

data want;
 do until(last.id);
  set have;
  by id;
  if not first.id then Timetoreadmission=Admitdate-_n_;
  _n_=DischargeDate;
  output;
 end;
run;