Macro returning a value

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;