Looping in SAS to bring the latest value - sas

Question

I am trying to find days matching to a reference number of days given or else to find the number of days close to the reference days.
I coded till here, however not sure how to go forward.
ID Date ref_days lags total_days
1 2017-02-02 224 . 0
1 2017-02-02 224 84 84
1 2017-02-02 224 84 168
2 2015-01-21 213 300 388
3 2016-02-12 560 95 .
3 2016-02-12 560 86 181
3 2016-02-12 560 82 263
3 2016-02-12 560 69 332
3 2016-02-12 560 77 409
So now I want to bring out the last value close to the reference days.
and the next total_days should start from ZERO again to find the next window. How can I do this?
Here is a code that I wrote
data want;
do until (totaldays <= ref_days);
set have;
by ID ref_days notsorted;
if first.id then totaldays=0;
else totaldays+lags;
end;
run;
Required Output:
ID Date ref_days lags total_days
1 2017-02-02 224 . 0
1 2017-02-02 224 84 84
1 2017-02-02 224 84 168
2 2015-01-21 213 300 388
3 2016-02-12 560 95 .
3 2016-02-12 300 86 181
3 2016-02-12 300 82 263
3 2016-02-12 300 69 .
3 2016-02-12 300 77 146

Answer 1

A while ago I did similar to this via Proc sql. It calculates all the distances and takes the closest one. It works with moderate size dataset. Hopefully it is of some use.
proc sql;
select * from
(
select *,
abs(t1.link-t2.link) as dist /*In your case these would be dateVars*/
from test1 t1
left join test2 t2
on 1=1) group by system1 having dist=min(dist);
;
quit;
There was some talk that the left join on 1=1 is a bit silly (as full outter join would suffice, or something.) However this worked for the problem in question.