Conditional flag by groups

[Miracle]

Dear Everyone,

May I please ask how do we get the last column, 'flag' given my input data containing id, date, vis and site?
I would like to be able to flag the most recent non-missing var from a visit given the date by site for patients.

Your help is very much appreciated.

id	date	vis	site	var	flag
1	01-Jan-2020	1	1		1
1	02-Feb-2020	2	1	10	1
1	03-Mar-2020	3	1	11	0
1	10-Mar-2020	3	1	12	1
1	05-Apr-2020	4	1	11	1
1	06-May-2020	5	1	9	1
1	07-Jun-2020	6	1	.	0
1	06-Jun-2020	6	1	13	1
1	09-Aug-2020	8	1	10	1
1	01-Jan-2020	1	2	9	1
1	02-Feb-2020	2	2	7	1
1	03-Mar-2020	3	2	5	1
1	10-Mar-2020	3	2	7	1
1	05-Apr-2020	4	2	8	1
1	06-May-2020	5	2	.	1
1	07-Jun-2020	6	2	7	1
1	25-Aug-2020	8	2	.	0
1	09-Aug-2020	8	2	10	1
2	01-Jan-2020	1	1	4	1
2	02-Feb-2020	2	1	10	1
2	03-Mar-2020	3	1	11	0
2	10-Mar-2020	3	1	12	1
2	05-Apr-2020	4	1	11	1
2	06-May-2020	5	1	9	1
2	07-Jun-2020	6	1	9	1
2	25-Jun-2020	7	1	13	1
2	09-Aug-2020	8	1	10	1
2	01-Jan-2020	1	2	9	1
2	02-Feb-2020	2	2	7	1
2	03-Mar-2020	3	2	5	0
2	10-Mar-2020	3	2	7	1
2	05-Apr-2020	4	2	8	1
2	06-May-2020	5	2	6	1
2	07-Jun-2020	6	2	7	1
2	31-Aug-2020	8	2	20	1
2	09-Aug-2020	8	2	10	0

[Kurt_Bremser]

With id = 1, site = 1, and vis = 3, you flag both observations as 1, but with id = 2, site = 2, vis = 8, you only flag the later as 1; what is the difference here?

[Miracle]

Thanks @Kurt_Bremser for pointing out.
Post is now corrected.

[Kurt_Bremser]

Try this:

proc sort data=have;
by id site vis date;
run;

data want;
set have;
by id site vis;
flag = last.vis;
run;

[Miracle]

Thanks @Kurt_Bremser  for trying to help 😊

I managed to get it done correctly by following this post here instead 

https://communities.sas.com/t5/SAS-Data-Management/create-a-flag-for-first-non-zero-observation-by-g...