SAS retain statement and existing variables

Question

I'm trying to understand how the retain statement is supposed to work with existing variables, but still it seems I missing something as I do not get the desired result

In the following example my code aim to create a sort of counter for the value variable

 data new (sortedby=id);
 input id $ value count;
 datalines ;
 d 55 0
 d 66 0
 d 33 0
 run;

 data cc;
 set new;
 by id;
 retain count;
 count+value;
 run;

And I 'm expecting that the count variable will be the result of the cumulation of the value column. However, the result is not achived and the column keep its original 0 values.

I would be interested in understanding why the implict retain statement in the "+" sign is not working in this case.

It is an issue related to the fact that count is an already existing variables?

Bests

Answer 1

All the RETAIN statement does is prevent variable from being set to missing at the top of the DATA step. In your code, your SET statement reads a value for COUNT (0), so even though the value is retained, it is reset to 0 when the SET statement executes.

I would play with code like below, with lots of PUT statements in it:

data cc;
   put "Top of loop" (_n_ value count count2 count3)(=) ;
   set new;
   put "After set statement " (_n_ value count count2 count3)(=) ;
   by id;
   retain count;
   count+value;
   count2+value ;
   count3=sum(count3,value) ;
   put "After sum statement" (_n_ value count count2 count3)(=) ;
run;

At the top of the loop, Count and Count2 are retained. Count is retained because of the explicit retain statement, and because it was read on a SET set statement. Count2 is retained because the sum statement has an implicit retain. Count3 is not retained.

Results are like:

Top of loop         _N_=1 value=.  count=.  count2=0  count3=.
After set statement _N_=1 value=55 count=0  count2=0  count3=.
After sum statement _N_=1 value=55 count=55 count2=55 count3=55

Top of loop         _N_=2 value=55 count=55 count2=55  count3=.
After set statement _N_=2 value=66 count=0  count2=55  count3=.
After sum statement _N_=2 value=66 count=66 count2=121 count3=66

Top of loop         _N_=3 value=66 count=66 count2=121 count3=.
After set statement _N_=3 value=33 count=0  count2=121 count3=.
After sum statement _N_=3 value=33 count=33 count2=154 count3=33
Top of loop         _N_=4 value=33 count=33 count2=154 count3=.