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What is a SAS macro

• A SAS macro is a named block of reusable code defined with `%macro` and ended with `%mend`
• Once defined, the macro is invoked by writing its name preceded by a percent sign — for example `%mymacro;`
• When SAS encounters a macro call, it replaces it with the code inside the macro definition before the program is compiled and run
• Macros reduce repetition: instead of writing the same block of code multiple times, you write it once inside a macro and call it wherever it is needed
• Macros can also accept parameters, making them adaptable to different inputs each time they are called
• The macro language is a separate layer that runs before SAS code — it generates SAS statements rather than running them directly

Macro variables versus macros

• A macro variable (covered in the macro variables lessons) stores a single text value and is referenced with `&name`
• A macro (this lesson) is a named block of code — it can contain DATA steps, PROC steps, logic, and macro variables all together
• Think of a macro variable as a text substitution, and a macro as a reusable subroutine

Basic macro syntax

• The definition starts with `%macro macroname;` and ends with `%mend macroname;`
• Everything between those two lines is the macro body — the SAS code that will be inserted when the macro is called
• The macro name in `%mend` is optional, but recommended because it makes long programs easier to read

/* %macro macroname; * SAS code goes here; %mend macroname; * Call the macro; %macroname; */ Copy Code View Log

A macro with no parameters

• The simplest macro runs the same fixed code every time it is called
• This is useful for setup steps such as setting options, printing a standard header dataset, or running a recurring quality check
• The macro below prints the current date and a short message to the log each time it is called

%macro print_today; data _null_; today = today(); format today date9.; put 'Today is: ' today date9.; run; %mend print_today; %print_today; %print_today; Copy Code View Log

• The macro is defined once, but called twice — check the SAS log and confirm that the date message appears twice
• The two calls produce identical output because there are no parameters — the same code runs each time

A macro with parameters

• Parameters make a macro flexible — they are named placeholders in the macro definition that receive values when the macro is called
• Parameters are listed inside parentheses after the macro name in the `%macro` line, separated by commas
• Inside the macro body, parameters are referenced as macro variables using the `&name` syntax
• At the call site, values are passed inside parentheses matching the parameter names

%macro print_obs(dsn=, n=5); proc print data=&dsn.(obs=&n.) noobs; run; %mend print_obs; %print_obs(dsn=sashelp.class, n=3); %print_obs(dsn=sashelp.cars, n=5); Copy Code View Log

• The first call prints 3 observations from SASHELP.CLASS, and the second prints 5 from SASHELP.CARS
• The same macro definition handles both because the dataset name and row count are passed as parameters
• The `=` syntax in the parameter list sets default values — `n=5` means that if `n` is not passed, 5 is used automatically

Default parameter values

• When a default is specified in the macro definition, the caller does not need to provide that parameter
• If the caller omits a parameter that has no default, it resolves to an empty string, which may cause syntax errors — so always provide sensible defaults or document which parameters are required
• The example below shows a call that omits `n` and therefore uses the default value of 5

%print_obs(dsn=sashelp.class); Copy Code View Log

• This call produces 5 rows from SASHELP.CLASS because `n` was not supplied and the default of 5 was used
• Compare the output with the earlier call that passed `n=3` to confirm the difference

A practical macro - summarise a variable in any dataset

• The macro below uses PROC MEANS to summarise a chosen numeric variable from any dataset
• Three parameters control the behaviour: the dataset name, the variable to summarise, and the output dataset name
• This is a common pattern in real programs, where the same summary logic is needed for multiple variables or domains

%macro summarise(dsn=, var=, out=summary); proc means data=&dsn. noprint; var &var.; output out=&out. mean= std= min= max= n= / autoname; run; %mend summarise; %summarise(dsn=sashelp.class, var=height, out=height_summary); %summarise(dsn=sashelp.class, var=weight, out=weight_summary); Copy Code View Log

• Two summary datasets are created from two macro calls with different `var` and `out` values
• Inspect `height_summary` and `weight_summary` and confirm that the statistics match expectations for the SASHELP.CLASS data
• Notice how the macro call is much shorter than writing two separate PROC MEANS steps with different variable names

View Data

Conditional logic inside a macro using %IF %THEN %ELSE

• Macros can contain `%if` / `%then` / `%else` statements that evaluate conditions at macro execution time
• These are macro-level statements and run before any SAS DATA step or PROC step is executed
• A common use is to choose between two different code paths based on a parameter value

%macro describe(dsn=, method=print); %if &method. = print %then %do; proc print data=&dsn.(obs=5) noobs; run; %end; %else %if &method. = contents %then %do; proc contents data=&dsn.; run; %end; %else %do; %put WARNING: Unknown method value &method. Use print or contents; %end; %mend describe; %describe(dsn=sashelp.class, method=print); %describe(dsn=sashelp.class, method=contents); %describe(dsn=sashelp.class, method=invalid); Copy Code View Log

• The first call runs PROC PRINT, the second runs PROC CONTENTS, and the third triggers the `%else` warning branch
• Check the SAS log — the third call should produce a WARNING message written by `%put`, but no SAS procedure output
• `%put` writes text directly to the SAS log and is very useful for debugging macro behaviour

Key points to remember

• Define macros with `%macro name;` and end with `%mend name;` — call them with `%name;`
• Parameters are listed in parentheses after the macro name and referenced inside the body as `&name`
• Default values in the parameter list make parameters optional at the call site
• Use `%if` / `%then` / `%else` / `%do` / `%end` for conditional macro logic — these run at macro execution time, before SAS compiles the generated code
• `%put` writes messages to the SAS log and is the primary macro debugging tool
• Macros do not return values — they generate SAS code that is then executed by SAS