code/retain value after trigger event

[wwjsun]

ID	Date	Glucose_elev	Gluose_historical
1	Jan-12	0	0
1	Mar-12	0	0
1	Oct-13	1	1
1	Feb-14	0	1
1	Jul-15	1	1
2	Feb-12	1	1
2	May-13	1	1
2	May-15	1	1
2	May-16	1	1
3	Jan-12	0	0
3	Feb-13	1	1
3	Jun-13	0	1
3	Feb-14	0	1
3	May-15	0	1
3	Nov-15	1	1
3	Dec-15	1	1
3	Dec-15	0	1

I'm working on a dataset contains multiple subjects' longitudinal glucose level.  A typical scenario is, a high-risk patients' glucose level maintain normal until it reached the level of diabetics stage (Glucose_elev=1). Once the event triggered, even afterward his blood glucose went under control by medicine (Glucose_elve=0), we still consider this individual as "diabetic" (Glocuse_historical=1) after initial trigger event and ever after.  Some of the patients may never reach to diabetics stage during the study; others may be diabetic all the way, like subject #2. 

I would like to know how to code for Glucose_historical value. For one subject, before the trigger event, Glucose_histroical= 0, and on and after the trigger event, Glucose_historical=1. 

Thanks a million

[Shmuel · Accepted solution]

try next code:

data want;

 set have;

  by ID;

        retain glucode_historical;

       if first.id then glucose_historical=0;

       if glucose_elev=1 then glucose_historical=1;

 run;

[wwjsun]

Absolutely! Thanks so much, Shmuel!