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Marching through the Macro Minefield

Marching through the Macro Minefield. Matthew Rodger Modelling Manager NAB matthew. d. rodger@ nab .com.au. Why use macros . If you have repetitive code ( %DO i= 1 %TO &noruns %BY 1 ; ) If you want conditional code ( %IF &run=y %THEN %DO ; )

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Marching through the Macro Minefield

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  1. Marching through the Macro Minefield Matthew Rodger Modelling Manager NAB matthew.d.rodger@nab.com.au

  2. Why use macros • If you have repetitive code (%DO i=1%TO &noruns %BY1;) • If you want conditional code (%IF &run=y %THEN%DO;) • Creating macro functions that can be re-used for other programs (%MACRO mymacro(parm1,...,parmn); ...%MEND;).

  3. Macro variables • Macro variables are different to defined macros and the two should not be confused • To create a macro variable, you can use %LET or CALL SYMPUT or PROCSQL. For example%LET presentation_date='05Mar2007'd; • Also defined in macro loops (be careful with nested loops) • Be careful of variable scope

  4. Macro variable uninitialised • This is a standard error308 %LET y=&t;WARNING: Apparent symbolic reference T not resolved. • You may be sure that you have defined the variable, but how can you be sure that it is actually defined? • It could also be a scope problem.

  5. Macro variable uninitialised • In some cases, you may wish the macro string to be resolved in an actual string, to do this, your string must be enclosed by double quotes. • If you use single quotes, then you will get & and the macro variable name, not the contents of the macro variable.

  6. Macro variable scope • If a macro variable is defined within a macro, it will only be known within that macro • If you want to see this macro variable outside of the macro, then you will need to use %GLOBAL • Inside a macro, you can see all global macro variables and you CAN change them, so be careful. • Don’t start macro variable names with SYS as there are many already defined

  7. Standard de-bugging tools • MPrint – All a macro essentially does is write SAS code. So by using the MPrint option, SAS will write in the log, the SAS code being executed • Symbolgen – This is what a macro variable and macro token resolve to • MLogic – This should display the results of a macro condition or loop i.e. %IF &run=y %THEN%DOor %DO j=1%TO &numvars.

  8. Standard Debugging tools • To turn these debugging tools off, then you can use OPTIONS NoMPrint NoSymbolgen NoMLogic • To know if these settings are on, then look in SASHELP.VOPTION • You can also use %PUT to put the value of a macro variable into the log. You don’t need a datastep to this, unlike a normal PUT, so this is very handy. • For example: %PUT &y

  9. Can I find a list of what all of my macro variables resolve to? • You can, plus all system defined macro variables. • In the SASHELP library, there are views and datasets with all sorts of useful SAS settings information in it. The file we are after is SASHELP.VMACRO • We can use this dataset to determine whether a variable has actually been declared and what value it takes

  10. I thought that comments were good • They are, but be very careful about how you type comments in a macro. • If you have a single quote (‘) in a * comment, then you will a unfinished quote and you code will not compile. • In a macro, it is best to use %* style comments

  11. Special macro functions • If you use %STR, then you won’t get the SAS meaning, you will just get the string instead • You can use %EVAL and %SYSEVALF if you want to evaluate an equation which involves a macro variable and dump the resulting output.

  12. What happens if the compiled macro name is not resolved and I want to know if it exists? • Your macro names are stored in a format. You can use PROCCATALOG and PROCSQL to determine what macros you can use.

  13. Another common mistake is to confuse macro code with standard SAS code • For example, you might use IF instead of %IF. • In some cases, your macro will compile and appear to work as it is not a syntax error. • This is a logical error and can be very hard to debug. • Normal SAS code is not chromocoded in SAS macros

  14. Additional white space in a macro string can be annoying • Using CALL SYMPUT and PROCSQL can assign a macro variable with additional whitespace. • You can instead use CALL SYMPUTX. • Code demonstration

  15. Errors in defined macro • If you have errors in your defined macro, then in some cases SAS will define a dummy macro. Other cases, it will not be compiled until there are no syntax errors.

  16. The End

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