Macros are powerful tools in SAS programming, especially in SDTM (Study Data Tabulation Model) programming, where they can automate repetitive tasks and ensure consistency across datasets. However, debugging macros can be challenging due to their complexity and the way they handle data. This guide provides detailed strategies and examples for effectively debugging macros in SDTM programming.

1. Use the MPRINT Option to Trace Macro Execution

The MPRINT option in SAS helps trace the execution of macro code by printing the SAS statements generated by the macro to the log. This is especially useful when you want to see the resolved code that the macro generates.

Example: Consider a macro that generates an SDTM domain. By enabling MPRINT, you can see exactly what code is being executed, helping you identify where errors might occur.

options mprint;

%macro create_dm;
   data dm;
      set rawdata;
      usubjid = subject_id;
      age = input(age_raw, 8.);
      sex = gender;
      /* More variable mappings */
   run;
%mend create_dm;

%create_dm;

With MPRINT enabled, the log will show the actual data step code generated by the macro, making it easier to identify any issues.

2. Use the MLOGIC Option to Debug Macro Logic

The MLOGIC option prints information about the macro’s logic flow, including when macros are called, when macro variables are resolved, and the values they resolve to. This helps you understand the macro’s decision-making process.

Example: Use MLOGIC to trace how a macro variable is being resolved within a loop or conditional statement.

options mlogic;

%macro check_age;
   %let min_age = 18;
   %let max_age = 65;

   %if &min_age > &max_age %then %do;
      %put ERROR: Minimum age cannot be greater than maximum age.;
   %end;
   %else %do;
      data age_check;
         set rawdata;
         if age >= &min_age and age <= &max_age then valid_age = 1;
         else valid_age = 0;
      run;
   %end;
%mend check_age;

%check_age;

With MLOGIC enabled, the log will show how the macro variables min_age and max_age are being resolved and the flow of logic within the macro.

3. Use the SYMBOLGEN Option to Track Macro Variable Resolution

The SYMBOLGEN option prints the resolution of macro variables to the log. This is particularly useful for debugging issues related to macro variable values, especially when those variables are used in data steps or PROC SQL.

Example: If a macro is not producing the expected results, use SYMBOLGEN to check how each macro variable is being resolved.

options symbolgen;

%macro filter_by_sex(sex=);
   data filtered;
      set dm;
      where sex = "&sex.";
   run;
%mend filter_by_sex;

%filter_by_sex(sex=M);

The log will show how the sex variable is being resolved, helping you confirm that the correct value is being passed to the where statement.

4. Incorporate PUTLOG Statements for Custom Debugging

While MPRINT, MLOGIC, and SYMBOLGEN provide automatic logging, adding PUTLOG statements within your macros allows for custom debugging messages. This can be particularly helpful when you need to check specific conditions or values during macro execution.

Example: Use PUTLOG to debug a conditional macro that applies different transformations based on input parameters.

%macro transform_data(var=, method=);
   %if &method = log %then %do;
      data transformed;
         set rawdata;
         &var._log = log(&var.);
         putlog "NOTE: Log transformation applied to " &var=;
      run;
   %end;
   %else %if &method = sqrt %then %do;
      data transformed;
         set rawdata;
         &var._sqrt = sqrt(&var.);
         putlog "NOTE: Square root transformation applied to " &var=;
      run;
   %end;
   %else %do;
      %put ERROR: Invalid method specified. Use "log" or "sqrt".;
   %end;
%mend transform_data;

%transform_data(var=height, method=log);

The PUTLOG statement will output a note to the log indicating which transformation was applied, or an error message if an invalid method was specified.

5. Test Macros with Simple, Controlled Inputs

Before using a macro in a complex scenario, test it with simple, controlled inputs to ensure it behaves as expected. This helps isolate the macro's functionality and identify potential issues in a controlled environment.

Example: Test a macro that standardizes date formats with a small sample dataset to ensure it handles various date formats correctly.

data test_dates;
   input rawdate $10.;
   datalines;
2021-01-01
01JAN2021
2021/01/01
;
run;

%macro standardize_date(datevar=);
   data standardized;
      set test_dates;
      format &datevar yymmdd10.;
      &datevar = input(&datevar, anydtdte10.);
   run;

   proc print data=standardized;
   run;
%mend standardize_date;

%standardize_date(datevar=rawdate);

This example demonstrates testing a date standardization macro with a simple dataset to ensure it correctly processes different date formats.

6. Break Down Complex Macros into Smaller Components

Complex macros can be challenging to debug due to the multiple steps and logic involved. Breaking down a complex macro into smaller, more manageable components makes it easier to identify and fix issues.

Example: Instead of writing a single macro to process an entire SDTM domain, split it into smaller macros that handle specific tasks, such as variable mapping, data transformation, and output formatting.

%macro map_variables;
   data mapped;
      set rawdata;
      usubjid = subject_id;
      age = input(age_raw, 8.);
      sex = gender;
   run;
%mend map_variables;

%macro transform_data;
   data transformed;
      set mapped;
      if age < 18 then age_group = 'Child';
      else age_group = 'Adult';
   run;
%mend transform_data;

%macro output_data;
   proc print data=transformed;
   run;
%mend output_data;

%map_variables;
%transform_data;
%output_data;

This approach makes it easier to debug each step individually and ensures that each component works correctly before combining them into a larger process.

7. Use Macro Quoting Functions to Handle Special Characters

Special characters in macro variables can cause unexpected behavior. Macro quoting functions like %STR, %NRSTR, %QUOTE, and %NRQUOTE help handle these characters correctly.

Example: If a macro variable contains special characters like ampersands or percent signs, use macro quoting functions to prevent errors.

%let special_char_var = %str(50% discount);
%put &special_char_var;

%macro handle_special_chars(text=);
   %put NOTE: The text is: %quote(&text);
%mend handle_special_chars;

%handle_special_chars(text=Special &char handling);

The macro quoting functions ensure that special characters are handled correctly, preventing syntax errors or unexpected behavior.

8. Utilize the Debugger Macro

SAS provides a %DEBUGGER macro for debugging other macros. It allows you to step through a macro's execution and inspect variable values at each step.

Example: Use the %DEBUGGER macro to interactively debug a complex macro, inspecting variable values and execution flow in real-time.

%macro my_macro(var=);
   %local step1 step2;
   %let step1 = %eval(&var + 1);
   %let step2 = %eval(&step1 * 2);
   %put NOTE: Final value is &step2;
%mend my_macro;

/* Start the debugger */
%debugger my_macro(var=5);

The %DEBUGGER macro allows you to step through the execution of my_macro, inspect the values of step1 and step2, and identify any issues in the logic.

9. Generate Test Outputs for Verification

Generating intermediate outputs or log messages at key steps in your macro can help verify that each part of the macro is working correctly.

Example: Add steps to your macro that output temporary datasets or log specific values during execution, allowing you to verify that the macro is functioning as expected.

%macro process_data(var=);
   data step1;
      set rawdata;
      &var._step1 = &var. * 2;
   run;
   proc print data=step1;
   run;

   data step2;
      set step1;
      &var._step2 = &var._step1 + 10;
   run;
   proc print data=step2;
   run;
%mend process_data;

%process_data(var=age);

In this example, intermediate datasets step1 and step2 are printed, allowing you to verify the transformations applied to the age variable at each stage.

10. Maintain a Debugging Log for Complex Macros

For complex macros, maintain a debugging log where you document the issues encountered, the steps taken to resolve them, and any notes on how the macro behaves under different conditions. This log can be invaluable for future debugging efforts.

Example: Create a debugging log as you develop and test a macro, noting any issues with specific data inputs, unexpected behaviors, or areas of the code that required special handling.

/* Debugging Log for %process_data Macro
   - Issue: The macro fails when var contains missing values
   - Resolution: Added a check for missing values before processing
   - Note: The macro works correctly with both positive and negative values
   - Date: YYYY-MM-DD
   - Author: Your Name
*/
%macro process_data(var=);
   %if &var = . %then %do;
      %put ERROR: Missing value for &var.. Macro will not execute.;
      %return;
   %end;

   data processed;
      set rawdata;
      &var._processed = &var. * 2;
   run;
%mend process_data;

%process_data(var=age);

This debugging log helps keep track of the macro's development and any issues resolved along the way, providing a valuable resource for future maintenance or enhancements.

Conclusion

Macro debugging in SDTM programming can be challenging, but by using these techniques—such as enabling logging options, breaking down complex macros, using custom PUTLOG statements, and maintaining a debugging log—you can effectively troubleshoot and resolve issues in your macros. These practices not only help ensure that your macros run correctly but also enhance the overall quality and reliability of your SDTM programming.