Calculation of values that rely on a date variable - sql

Question

I am trying to calculate the value of the last measurement taken (according to the date column) divided by the lowest value recorded (according to the measurement column) if two values in the “SUBJECT” column match and two values in the “PROCEDURE” column match. The the calculation would be produced in a new column. I am having trouble with this and I would appreciate a solution to this matter.
data Have;
input Subject Type :$12. Date &:anydtdte. Procedure :$12. Measurement;
format date yymmdd10.;
datalines;
500 Initial 15 AUG 2017 Invasive 20
500 Initial 15 AUG 2017 Surface 35
500 Followup 15 AUG 2018 Invasive 54
428 Followup 15 AUG 2018 Outer 29
765 Seventh 3 AUG 2018 Other 13
500 Followup 3 JUL 2018 Surface 98
428 Initial 3 JUL 2017 Outer 10
765 Initial 20 JUL 2019 Other 19
610 Third 20 AUG 2019 Invasive 66
610 Initial 17 Mar 2018 Invasive 17
;
*Intended output table
Subject Type Date Procedure Measurement Output
500 Initial 15 AUG 2017 Invasive 20 20/20
500 Initial 15 AUG 2017 Surface 35 35/35
500 Followup 15 AUG 2018 Invasive 54 54/20
428 Followup 15 AUG 2018 Outer 29 29/10
765 Seventh 3 AUG 2018 Other 13 13/19
500 Followup 3 JUL 2018 surface 98 98/35
428 Initial 3 JUL 2017 Outer 10 10/10
765 Initial 20 JUL 2019 Other 19 19/19
610 Third 20 AUG 2019 Invasive 66 66/17
610 Initial 17 Mar 2018 Invasive 17 17/17 ;
*Attempt;
PROC SQL;
create table want as
select a.*,
(select measurement as measurement_last_date
from have
where subject = a.subject and type = a.type
having date = max(date)) / min(a.measurement) as ratio
from have as a
group by subject, type
order by subject, type, date;
QUIT;

Answer 1

I think that you need use statement retain with data step.
the statement will retain your last row and you can 'll compare the last row with actual row processed.
link of some tutorial of how use statement retain.
enter link description here
SAS documentation
enter link description here