Macro returning a value - sas

Question

I created the following macro. Proc power returns table pw_cout containing column Power. The data _null_ step assigns the value in column Power of pw_out to macro variable tpw. I want the macro to return the value of tpw, so that in the main program, I can call it in DATA step like:
data test;
set tmp;
pw_tmp=ttest_power(meanA=a, stdA=s1, nA=n1, meanB=a2, stdB=s2, nB=n2);
run;
Here is the code of the macro:
%macro ttest_power(meanA=, stdA=, nA=, meanB=, stdB=, nB=);
proc power;
twosamplemeans test=diff_satt
groupmeans = &meanA | &meanB
groupstddevs = &stdA | &stdB
groupns = (&nA &nB)
power = .;
ods output Output=pw_out;
run;
data _null_;
set pw_out;
call symput('tpw'=&power);
run;
&tpw
%mend ttest_power;

Answer 1

#itzy is correct in pointing out why your approach won't work. But there is a solution maintaing the spirit of your approach: you need to create a power-calculation function uisng PROC FCMP. In fact, AFAIK, to call a procedure from within a function in PROC FCMP, you need to wrap the call in a macro, so you are almost there.
Here is your macro - slightly modified (mostly to fix the symput statement):
%macro ttest_power;
proc power;
twosamplemeans test=diff_satt
groupmeans = &meanA | &meanB
groupstddevs = &stdA | &stdB
groupns = (&nA &nB)
power = .;
ods output Output=pw_out;
run;
data _null_;
set pw_out;
call symput('tpw', power);
run;
%mend ttest_power;
Now we create a function that will call it:
proc fcmp outlib=work.funcs.test;
function ttest_power_fun(meanA, stdA, nA, meanB, stdB, nB);
rc = run_macro('ttest_power', meanA, stdA, nA, meanB, stdB, nB, tpw);
if rc = 0 then return(tpw);
else return(.);
endsub;
run;
And finally, we can try using this function in a data step:
options cmplib=work.funcs;
data test;
input a s1 n1 a2 s2 n2;
pw_tmp=ttest_power_fun(a, s1, n1, a2, s2, n2);
cards;
0 1 10 0 1 10
0 1 10 1 1 10
;
run;
proc print data=test;

Answer 2

You can't do what you're trying to do this way. Macros in SAS are a little different than in a typical programming language: they aren't subroutines that you can call, but rather just code that generate other SAS code that gets executed. Since you can't run proc power inside of a data step, you can't run this macro from a data step either. (Just imagine copying all the code inside the macro into the data step -- it wouldn't work. That's what a macro in SAS does.)
One way to do what you want would be to read each observation from tmp one at a time, and then run proc power. I would do something like this:
/* First count the observations */
data _null_;
call symputx('nobs',obs);
stop;
set tmp nobs=obs;
run;
/* Now read them one at a time in a macro and call proc power */
%macro power;
%do j=1 %to &nobs;
data _null_;
nrec = &j;
set tmp point=nrec;
call symputx('meanA',meanA);
call symputx('stdA',stdA);
call symputx('nA',nA);
call symputx('meanB',meanB);
call symputx('stdB',stdB);
call symputx('nB',nB);
stop;
run;
proc power;
twosamplemeans test=diff_satt
groupmeans = &meanA | &meanB
groupstddevs = &stdA | &stdB
groupns = (&nA &nB)
power = .;
ods output Output=pw_out;
run;
proc append base=pw_out_all data=pw_out; run;
%end;
%mend;
%power;
By using proc append you can store the results of each round of output.
I haven't checked this code so it might have a bug, but this approach will work.

Answer 3

You can invoke a macro which calls procedures, etc. (like the example) from within a datastep using call execute(), but it can get a bit messy and difficult to debug.