SAS Macros¶
A SAS %macro is a discrete piece of code that can be accessed throughout the SAS script by keyword reference. A SAS %macro can take and use arguments. A SAS %macro is useful when you need to execute a similar set of tasks over and over again (for instance, over many years). This is similar to a program or ado in Stata or functions in R and Python. The general syntax is:
%macro name(/* Arguments go here */);
/* SAS code goes here */
%mend name;
A SAS %macro is referenced elsewhere in a SAS script as %name(...). You can think of a SAS %macro as inserting the contained text/statements into the SAS script whenever referenced.
Arguments¶
A SAS %macro has two types of arguments (or none at all): positional and keyword. Keyword arguments are specified with a keyword, equals sign and a default value (which can be null)
%macro name(keyward_arg = 1);
%mend name;
or with a null default value
%macro name(keyword_arg = );
%mend name;
To supply a custom value of 10 we we would would write
%name(keyword_arg = 10);
Positional arguments are just listed and are assigned the value corresponding to their position in the argument list when the macro is defined:
%macro name(a, b, c);
%mend name;
If I called %name(1, 2, 3) then a = 1, b = 2, c = 3. If no argument is specified in the corresponding position then the positional argument resolves to null.
Arguments are referenced inside of a %macro as macro variables. These concepts are illustrated below.
%macro hello_world;
%PUT Hello World!;
%mend hello_world;
%macro hello_place(place);
%PUT Hello &place.!;
%mend hello_place;
%macro hello_there(place, name = John);
%PUT Hello &place., my name is &name.!;
%mend hello_there;
%hello_world;
%hello_place(USA);
%hello_there(USA);
%hello_there();
%hello_there(USA, name = Danny);
These macro calls output
324 %hello_world;
Hello World!
325 %hello_place(USA);
Hello USA!
326 %hello_there(USA);
Hello USA, my name is John!
327 %hello_there();
Hello , my name is John!
328 %hello_there(USA, name = Danny);
Hello USA, my name is Danny!
Example¶
To motivate the use of %macro functions, suppose you needed to load in two years of data and generate a few variables. You could do something like:
data out.intergen_1999_clean;
set in.intergen_1999;
year = 1999;
par_inc = mom_inc + dad_inc;
run;
data out.intergen_2000_clean;
set in.intergen_2000;
year = 2000;
gen par_inc = mom_inc + dad_inc;
run;
However, you can also do this in a cleaner and more efficient way with a %macro function.
* Define our macro;
%macro clean_intergen(year);
data intergen_&year._clean;
set intergen_&year.;
year = &year.;
par_inc = mom_inc + dad+inc;
run;
%mend clean_intergen;
* Call the macro on each year;
%clean_intergen(1999);
%clean_intergen(2000);
This style of coding is preferred as it keeps our scripts concise, generally reduces errors and makes debugging easier.