carrying backward values in longitudinal data

[Baraso]

I have the data  below. 

data have ;
input id month enrol_period disenrollment reenrollment event case ;
cards ;
1 0 1 0 0 0 1
1 1 1 0 0 0 1
1 2 1 0 0 0 1
1 3 1 0 0 0 1
1 4 -1 1 0 0 1
1 5 -1 0 0 0 1
1 6 -1 0 0 0 1
1 7 2 0 1 0 1
1 8 2 0 0 0 1
1 9 2 0 0 0 1
1 10 2 0 0 1 1
2 0 1 0 0 0 0
2 1 1 0 0 0 0
2 2 1 0 0 0 0
2 3 1 0 0 0 0
2 4 1 0 0 0 0
2 5 1 0 0 0 0
2 6 1 0 0 0 0
2 7 1 0 0 0 0
2 8 1 0 0 0 0
2 9 1 0 0 0 0
2 10 1 0 0 0 0  ;
run;

I want to have the data below. The case status has been reset to 0, during the months which period is -1 and before. 

Multiple disenrollment and reenrollment can happen during follow-up. Event is one of the end-points of the study. If event happens, I want to consider it only for the last period of enrollment, not entire follow-up. 

data want ;
input id month enrol_period disenrollment reenrollment event case ;
cards ;
1 0 1 0 0 0 0
1 1 1 0 0 0 0
1 2 1 0 0 0 0
1 3 1 0 0 0 0
1 4 -1 1 0 0 0
1 5 -1 0 0 0 0
1 6 -1 0 0 0 0
1 7 2 0 1 0 1
1 8 2 0 0 0 1
1 9 2 0 0 0 1
1 10 2 0 0 1 1
2 0 1 0 0 0 0
2 1 1 0 0 0 0
2 2 1 0 0 0 0
2 3 1 0 0 0 0
2 4 1 0 0 0 0
2 5 1 0 0 0 0
2 6 1 0 0 0 0
2 7 1 0 0 0 0
2 8 1 0 0 0 0
2 9 1 0 0 0 0
2 10 1 0 0 0 0
;
run;

Any ideas to resolve this are appreciated. Thanks. 

[Jagadishkatam · Accepted solution]

Please try the below code

data have ;
input id month enrol_period disenrollment reenrollment event case ;
if enrol_period=-1 then newvar=month;
cards ;
1 0 1 0 0 0 1
1 1 1 0 0 0 1
1 2 1 0 0 0 1
1 3 1 0 0 0 1
1 4 -1 1 0 0 1
1 5 -1 0 0 0 1
1 6 -1 0 0 0 1
1 7 2 0 1 0 1
1 8 2 0 0 0 1
1 9 2 0 0 0 1
1 10 2 0 0 1 1
2 0 1 0 0 0 0
2 1 1 0 0 0 0
2 2 1 0 0 0 0
2 3 1 0 0 0 0
2 4 1 0 0 0 0
2 5 1 0 0 0 0
2 6 1 0 0 0 0
2 7 1 0 0 0 0
2 8 1 0 0 0 0
2 9 1 0 0 0 0
2 10 1 0 0 0 0  
;
run;

proc sort data=have;
by id descending newvar;
run;

data want;
set have;
by id descending newvar;
retain newvar2;
if first.id then newvar2=newvar;
if month<=newvar2 then case=0;
run;

proc sort data=want;
by id month;
run;

[Baraso]

Thank you so much Jag. This answer is exactly what I was looking for. 

I appreciate your help. 

Best, 

Bahareh