How to use retain statement to fill in IDs and other info?

[ginger2]

How to use retain to fill in the missing A and B and C
Here is the code so far to make this dataset:

data PROD_ALL;
set _PROD_ALL;
if B=strip('Subject ID') then delete;
if missing(G) then delete;
run;

[PaigeMiller]

/* UNTESTED CODE */
data want;
    set have;
    retain a1 b1 c1;
    if not missing(a) then a1=a;
    if not missing(b) then b1=b;
    if not missing(c) then c1=c;
run;

This code is untested, because we cannot work with data in a screen capture. To get tested code, please provide the data as working SAS data step code (instructions and examples).

[Ksharp]

/* UNTESTED CODE */
data have;
 set have;
 id=1;
run;
data want;
  update have(obs=0) have;
  by id;
  output;
run;