automatically retained

[fbl204653]

Hi SAS experts,

when I ran the following program, I found y was automatically retained for x=4 in data test2. What happed?

Thanks!

data test;
    input x y;
    cards;
    1 .
    3 .
    ;
run;

data test1;
    input x;
    cards;
    3
    4
    ;
run;
data test2;
    set test(in=a)
        test1(in=b);
    if b then do;
        if x=3 then y=4;
    end;
run;

[PGStats]

There is no y variable in dataset test1 so the value of y isn't reset to missing when test1 is read.

[fbl204653]

Thanks!

[PGStats]

My answer is not quite right. You should mark @Astounding answer as the correct answer instead.

[Astounding · Accepted solution]

Any variable that comes from any SAS data set is automatically retained.  Since Y comes from a SAS data set, it is automatically retained.

A small complication:  when switching data sets (from TEST to TEST1 in the SET statement), Y is reset to missing.  You can see that by adding this statement after the SET statement:

put Y;

But once Y is set to 4, it remains 4 (unless changed by subsequent programming statements).  As @PGStats said, reading an observation from TEST1 does not replace Y. 

[fbl204653]

Thanks!