RETAIN for Each BY

[Junyong]

Now I am multiplying the following numbers recursively.

data a;
input a b;
cards;
1 1.1
1 1.1
1 1.1
1 1.1
1 1.1
2 1.2
2 1.2
2 1.2
2 1.2
2 1.2
;
run;

I can use RETAIN to do this.

data a;
set a;
by a;
retain c 1;
c=c*b;
put c;
run;

The problem is, SAS multiplies all the numbers, while I want to apply RETAIN for each BY—restarting at the sixth here.

16   data a;
17   set a;
18   by a;
19   retain c;
20   if first.a then c=1;
21   c=c*b;
22   put c;
23   run;

1.1
1.21
1.331
1.4641
1.61051
1.2
1.44
1.728
2.0736
2.48832
NOTE: There were 10 observations read from the data set WORK.A.
NOTE: The data set WORK.A has 10 observations and 3 variables.
NOTE: DATA statement used (Total process time):
      real time           0.04 seconds
      cpu time            0.03 seconds

Is there any way to do this? By the way, I know that

if first.a then c=1;

works in this case, but I wonder whether RETAIN is directly applicable for each BY more generally—I tried IF FIRST.A THEN RETAIN C 1; here but did not work. Thanks.

[novinosrin]

Is there any way to do this? By the way, I know that

if first.a then c=1;

works in this case, but I wonder whether RETAIN is directly applicable for each BY more generally—I tried IF FIRST.A THEN RETAIN C 1; here but did not work. Thanks.

Of course won't work because RETAIN  is a compile time statement whereas IF THEN is an execution time statement. Are you looking for something fancy?

[novinosrin]

Or you could mimic a retain to make it seem like as though you declared only once with a DOW loop

data a;
c=1;
do until(last.a);
set a;
by a;
c=c*b;
put c;
end;
run;

Nevertheless, I see no value regardless

[novinosrin]

Something I fancied to get your results

data a;
set a;
by a;
if first.a then grp=1;
else grp+1;
c=b**grp;
put c;
run;

[ErikLund_Jensen · Accepted solution]

Hi @Junyong 

Retain is a compile-time statement, and it just tells SAS not to reset the value to missing before each input record is read. It is not necessary to supply a value to supply a value in the retain statement.

So everything works if you assign the value of b to c in the first observation in each by group:

data b;
	set a;
	by a;
	retain c;
	if first.a then c = b;
	else c = c * b;
run;