SAS date/time

[monday89]

HI. I have the following table below. If the subject has start DATE is different or at a later date of stop date, I would like to cut the stop date to END at before midnight before the next day. If not, keep the same stop date. I have no idea how to start. I tried to break the start date and time as only date and then see if it start date= stop date, then keep stop date. If not then use midnight of that date. but it was pretty long. 

SubjectID	start_date_time	stop_date_time	formGroup
1	21NOV19:18:04:00	22NOV19:17:30:00	Day 1
1	22NOV19:17:30:00	23NOV19:14:46:00	Day 2
2	11NOV19:04:22:00	11NOV19:05:00:00	Day 1
2	11NOV19:05:00:00	12NOV19:01:00:00	Day 1
2	12NOV19:01:00:00	12NOV19:08:25:00	Day 2

New dataset:
 

SubjectID	start_date_time	stop_date_time	formGroup	New_stop_date
1	21NOV19:18:04:00	22NOV19:17:30:00	Day 1	21NOV19:23:59:59
1	22NOV19:17:30:00	23NOV19:14:46:00	Day 2	22NOV19:23:59:59
2	11NOV19:04:22:00	11NOV19:05:00:00	Day 1	11NOV19:05:00:00
2	11NOV19:05:00:00	12NOV19:01:00:00	Day 1	11NOV19:23:59:59
2	12NOV19:01:00:00	12NOV19:08:25:00	Day 2	12NOV19:08:25:00

[PaigeMiller]

Why is the fourth row of the output data set have new_stop_date 12NOV19:23:59:59 and not 11NOV19:23:59:59 ??

[monday89]

Good catch. I'll fix it!

[PaigeMiller]

data want;
    set have;
    if datepart(stop_date_time)>datepart(start_date_time) then 
        new_stop_date=hdms(datepart(start_date_time),23,59,59);
    else new_stop_date=stop_date_time;
run; 

Suggestion: spend some time reading the SAS documentation regarding date and datetime and time functions. https://documentation.sas.com/?cdcId=pgmmvacdc&cdcVersion=9.4&docsetId=allprodslang&docsetTarget=syn...