Conditional Subtraction within the same column using SAS - sql

Question

here is a portion of a data set I have named “antibody” :
Row Subject Type Procedure Measurement Output
1 500 Intial Invasive 20 20
2 500 Initial Surface 35 35
3 500 Followup Invasive 54 54-20
4 428 Followup Outer 29 29-10
5 765 Seventh Other 13 13-19
6 500 Followup Surface 98 98-35
7 428 Initial Outer 10 10
8 765 Initial Other 19 19
9 610 Third Invasive 66 66-17
10 610 Initial Invasive 17 17
I was trying to use proc sql to perform this. The goal is to subtract the numbers in the "MEASUREMENT" column based on the "SUBJECT", "TYPE" and “PROCEDURE” columns. If two values in the “SUBJECT” column match and two values in the “PROCEDURE” column match, then the initial measurement should be subtracted from the other measurement. For example, the initial measurement in row 1 (20) should be subtracted from the followup measurement in row 3 (54) because the subject (500) and procedure (Invasive) match. Furthermore, the initial measurement in row 8 (19) should be subtracted from the seventh measurement in row 5 (13) because the subject (765) and procedure (Other) match. The result should form the "OUTPUT" column.
Thank you in advance!

Answer 1

Here is a hash object approach
data have;
input Subject Type $ 5-12 Procedure $ 15-22 Measurement;
datalines;
500 Initial Invasive 20
500 Initial Surface 35
500 Followup Invasive 54
428 Followup Outer 29
765 Seventh Other 13
500 Followup Surface 98
428 Initial Outer 10
765 Initial Other 19
610 Third Invasive 66
610 Initial Invasive 17
;
data want (drop=rc _Measurement);
if _N_ = 1 then do;
declare hash h (dataset : "have (rename=(Measurement=_Measurement) where=(Type='Initial'))");
h.definekey ('Subject');
h.definedata ('_Measurement');
h.definedone();
end;
set have;
_Measurement=.;
if Type ne 'Initial' then rc = h.find();
Measurement = sum (Measurement, -_Measurement);
run;
EDIT:
data want (drop=rc _Measurement);
if _N_ = 1 then do;
declare hash h (dataset : "have (rename=(Measurement=_Measurement) where=(Type='Initial'))");
h.definekey ('Subject');
h.definedata ('_Measurement');
h.definedone();
end;
set have;
_Measurement=.;
if Type ne 'Initial' then rc = h.find();
NewMeasurement = ifn(Measurement=., ., sum (Measurement, -_Measurement));
run;