macro within a macro

[irisirissy]

I have a trouble understanding a code like below:

%let hi=;

%macro hi(a);

data test_&a;

set kk;

where class=a;

run;

%let hi=&hi test_&a;

%mend;

%hi(1)

%hi(2)

%hi(3)

what does the code in underline do? 

[PeterClemmensen]

It is simple macro variable definition. it Overrides the macro variable set at the top by the same name of hi and adds another string containing the string 'test_' and the macro variable a, which is the parameter given to the macro in the parenthesis in hi(a).

[RW9]

Its really not very good programming.  Several reasons.  First the macro really doesn't do anything other than split your data out - which is rarely a good idea anyway, but in doin git this way obfuscates the code somewhat:

data test_1 test_2 test_3;
  set kk;
  select(a);
    when 1 output test_1;
    when 2 output test_2;
    otherwise output test_3;
  end;
run;

Is effectively the same.

The code is also incorrect as you give it, unless there is a variable called a in the dataset kk, it will not work, I assumed you meant &a?

Now if you add a %put statement into the macro you will clearly see what the %let is doing, it is building a list of space delimited dataset names e.g.

test_1 test_2 test_3

I assume this is so you can use that list to process further - again, because of the programming choice to split your data up you then have to start adding lots of code to try to process multiple datasets - more work, harder to maintain etc.  Use one dataset and use by group processing - this is what it is for,

Finally, you are telling SAS that the hi macro is global, and then adjusting it within a macro.  In this simple example it may work, but doing something like this can lead to very hard to debug problems later on - when code may not even be in the same file etc.  Again, not a good idea.  Unless there is a good reason, follow encapsulisation and keep scope local.

This is the program (with some readability added - very important):

%let hi=;
%macro hi(a);
  data test_&a.;
    set sashelp.class;
    where age=&a.;
  run;
   
  %let hi=&hi test_&a.;
  %put &hi.;
%mend;
 
%put &hi.;

%hi(12)
%hi(15)
%hi(16)