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SAS: Macros

SAS: Macros. Computing for Research I Spring 2014 January 22, 2014. Why learn SAS macros?. Avoid repetitious SAS code Create generalizable and flexible SAS code Pass information from one part of a SAS job to another Conditionally execute data steps and PROCs

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SAS: Macros

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  1. SAS: Macros Computing for Research I Spring 2014 January 22, 2014

  2. Why learn SAS macros? • Avoid repetitious SAS code • Create generalizable and flexible SAS code • Pass information from one part of a SAS job to another • Conditionally execute data steps and PROCs • Dynamically create code at execution time

  3. Pros and Cons of Macros • Pros • Coding time – once familiar with macros • Updates – will propagate throughout code • Validation – only needs to be done once • Allows data-driven conditional processing • Cons • Initial coding is more complex • May take longer to compile or execute

  4. The SAS Macro Facility • A tool for text substitution • Simple text strings or SAS language statements • A component of Base SAS • May be used with SAS procedures, graphics, data steps, ODS, etc. • Facility has two main components • Macro processor – portion of SAS that does the work • Macro language – syntax that communicates with the processor

  5. The SAS Macro Facility Macro statements Standard SAS statements Macro processor

  6. Activating the Macro Processor • Macro Variable • Syntax: &name • Refers to a macro variable name reference • Processor completes the text substitution • Macro • Syntax: %name • Refers to a macro call • Processor compiles the macro with text substitution

  7. Learning Macro Coding • Beginner Tips • Creating macro variables for text substitution • Dynamic macro variables using data • Defining and calling macros • Conditional processing using macros • Iterative processing using macros

  8. Beginner Tips • Read your LOG • Turn on system options to view text substitution and macro execution notes • Syntax: OPTIONS MPRINT SYMBOLGEN; • Default is NOMPRINT and NOSYMBOLGEN • Allows validation of code and aids in debugging • Focus on the program then incorporate the macros • Plan out your program before you start coding • Write syntax that works • Supplement the syntax with macros for efficiency

  9. Macro Variables: System • SAS opening triggers several automatic macro variables • Global: these variables are available at any time in the session in any part of the code • User-defined variables may be added to global symbol table • Minimum length of 0 (missing) • Maximum length of 65,534 characters • Stores numeric values as character strings

  10. Macro Variables: System SYSCMD LAST NON-SAS COMMAND ENTERED SYSDATE CURRENT DATE IN DATE6. OR DATE7. FORMAT SYSDAY CURRENT DAY OF THE WEEK SYSDEVIC CURRENT GRAPHICS DEVICE SYSDSN LAST SAS DATASET BUILT SYSINDEX NUMBER OF MACROS STARTED IN JOB SYSINFO SYSTEM INFORMATION GIVEN BY SOME PROCS SYSPROD INDICATES WHETHER A SAS PRODUCT IS LICENSED SYSSCP OPERATING SYSTEM WHERE SAS IS RUNNING SYSTIME STARTING TIME OF JOB SYSVER SAS VERSION

  11. Macro Variables: System • Display all automatic system macro variables after opening SAS • Syntax: %put _automatic_; • The following will appear in the SAS log after submitting the above code: AUTOMATIC SYSDATE 21JAN14 AUTOMATIC SYSDATE9 21JAN2014 AUTOMATIC SYSDAY Tuesday AUTOMATIC SYSTIME 17:45 AUTOMATIC SYSVER 9.2

  12. Using System Macro Variables • May want to include a run date on reports • “Report run as of January 21, 2014.” • Macro variables references begin with anampersand (&) followed by a macro variable name • Syntax: &sysdate9 • To create a footnote with a run date: • Syntax: footnote1 “Report run as of &sysdate9”; • Output: Report run as of 21JAN2014 • Log: Macro variable SYSDATE9 resolves to 21JAN2014

  13. Macro Variables: General • An efficient way of replacing text strings in SAS code. • Can be defined within a macro definition or within a statement that is outside a macro definition, referred to as OPEN code. • Are independent of SAS data set variables.

  14. Macro Variables: User Defined • Create your own macro variables • Helpful to include these at the top of the program or to create instructions at the top of the program of which variables will need updated • Global macro variable creation • %LET statement will create a macro variable • Syntax: %LET newvar=January 1, 2014; • The macro variable “newvar” now contains the text “January 1, 2014” • Syntax: title “Data as of &newvar”; • Output: Data as of January 1, 2014

  15. Macro Variables: Rules • Naming Conventions • Must start with a letter or _ • Can be followed by letters or digits • Cannot be a reserved word • http://support.sas.com/documentation/cdl/en/mcrolref/61885/HTML/default/viewer.htm#a001958322.htm • Cannot start with SYS, AF, or DMS • Defining the value of the macro variable • May be character or numeric • Do not use quotes around text

  16. Using Macro Variables • Call the macro variable with the ampersand and the variable name • May be called from statements such as title or footnote, within data steps, and in procedures • Syntax: &newvar • Using quotes around a macro variable • Text statements such as title that call a macro variable must use double quotes (“) • The macro variable will not resolve if placed inside single quotes (‘) • Example

  17. Using Macro Variables • Macro variables can also be used in both DATA steps and PROCs (procedures) • Can be used for numeric or character values • Only use quotes around the macro variable name if quotes would be used without macros • Always use double quotes • Example

  18. Macro Variable Resolution • The ampersand & tells SAS that the text following it is a macro variable name • SAS considers all text following & to be part of the macro variable name until it encounters another & or other delimiter such as “ or ; • A period . can be used as a delimiter to separate a macro variable name from text • If a period is part of the text then include two periods

  19. Macro Variable Resolution • Examples of the use of delimiters for macro variables in text • %let var1=final; • %let var2=exam;

  20. Macro Variables: Part Two • SAS frequently allows for more than one way to do things • The SYMPUT routine can also create macro variables • Can be used to create macro variables with static values or dynamic (data dependent) values • Creates a global variable if created in open code (outside a macro) similar to %let • Syntax: CALL SYMPUT(“macro variable name”,text); • If text appears in quotes then it is a literal value. If it appears without quotes as it does here, then it is a variable name.

  21. Call Symput Example • You create a report with multiple data listing tables. You receive a request to have the title of each table contain the number of observations. • Example: A listing of hundreds of Adverse Events • Write code to count the total observations in the table • Syntax: procsql; create table total as select count(*) as freq from aetable; quit; • Create a macro variable that contains the total • Syntax: data _null_; set total; call symput(“tot”,freq); run; • Create a title statement that calls the macro variable • Syntax: title “This is the AE Listing (N=&tot.)”; • Output: This is the AE Listing (N=100)

  22. Defining Macros • A macro enables you to write macro programs • Programs will enable you to do iterative and conditional processing • General syntax of a macro or macro definition: • %MACRO macro_name; macro_text %MEND macro_name;

  23. Defining Macros • Macro name follows SAS variable naming conventions – identifies the macro • Macro text may include text, SAS statements, and macro variables, functions, or calls • After submitting a macro definition: • Macro language statements are checked for syntax errors and compiled • SAS statements are not checked for syntax errors

  24. Calling a Macro • Calling a macro causes it to execute • Call can be made anywhere in the program after the macro has been defined • Represents a macro trigger • Syntax for calling a macro: • % macro_name • Note that a semi-colon is not needed after the macro call

  25. Defining Macro Parameters • Macros with keyword parameters • There are other types of parameters but these are the most easily identified in code • Syntax: %MACRO macro_name(keyword=value,…,keyword=value); macro text %MEND macro_name; • Keyword parameters • Can be specified in any order • Are assigned a default or null value after equal sign • Are local macro variables (as opposed to global) • They can only be called within the specified macro

  26. Macro Example • You need to be able to output the grade distribution by gender and type of sport for athletes at your college as quickly as possible. • Original Syntax: procfreq data=grades; where gender=“Male” and sport=“Football”; table grades; title “Grade Distribution for Male Football Players”; run;

  27. Macro Example • Define the macro syntax: %macro grade(gender=,sport=); procfreq data=grades; where gender=“&gender” and sport=“&sport”; table grades; title “Grade Distribution for &gender. &sport. Players”; run; %mend grade; • Call the macro: %grade(gender=Male,sport=Football)

  28. Macro Example 2 • Create a customized graph of drug levels in the blood over time for several cohorts and dose levels, but not all • Original Syntax: title “Cohort 1, Dose Level 1 Drug Levels Over Time”; procgplot data=new(where=(cohort=1 and dose=1)); plot dose_one_level*time; run; quit; • This syntax would need repeated for each cohort and dose level necessary

  29. Macro Example 2 • Macro Syntax: %macro doses (cohort=,dose=,num=); title “Cohort &cohort., Dose Level &dose. Over Time”; procgplot data=new(where=(cohort=&cohort. and dose=&dose.)); plot dose_&num._level*time; run; quit; %mend doses; %doses(cohort=1,dose=1,num=one) %doses(cohort=1,dose=2,num=two)

  30. Keys to Macro Development • Write and debug the SAS program without macro coding • Generalize by removing hardcoded constants and creating macro variables with %LET statements • Define a macro by placing %MACRO and %MEND statements around the program • Convert %LET statements to macro parameters

  31. Using Macros: Conditional Processing • Defining a macro allows you to use conditional processing outside of the data step • IF, THEN, ELSE, DO, END • Conditional keywords must have the % sign in front of them inside the macro definition • %IF, %THEN, %ELSE, %DO, %END • AND/OR are exceptions • This enables you to execute certain portions of the code based on the data

  32. Conditional Processing Example • You are creating a report with numerous tables by injury type. The reports for each injury type have identical information, however, the lab values are stored in different tables for each injury type. Run the report program to create a report by injury type using conditional processing. • Injury types: severe, mild • Respective lab table names: form01, form02

  33. Conditional Processing Example %MACRO report(injurytype=,num=); %IF &injurytype=severe %THEN %DO; data labs; set form01; run; %END; %ELSE %IF &injurytype=mild %THEN %DO; data labs; set form02; run; %END; proc means data=labs n mean std; varinr creatinine; run; quit; %MEND report; %report(injurytype=severe) %report(injurytype=mild)

  34. Using Macros: Iterative Processing • Iterative processing can be done within a macro definition • Can repeatedly execute macro statements • Can repeatedly generate SAS code • Keywords enable the processing • %DO, %END, %BY • The index variable (%I) is a macro variable • %START and %STOP macro variables are available

  35. Iterative Processing Example • Your client requests that a dataset be created for each subject. You have several hundred subjects in your study. How can you do this efficiently? • Use iterative processing and macro variables to create a loop that output the data for each subject into its own dataset

  36. %macrosubs; procsql; create table total as select count(distinct subject) as total_subjects from masterdata; quit; data _null_; set total; call symput ('total',total_subjects); run; %do i=1 %to &total; data sub&i; set masterdata; if _n_=&i; run; %end; %mend subs; %subs

  37. Wrap-Up • Programming in SAS using macros can make your life easier • Reduces updates throughout programs • Reduces repetitious code • Allows for conditional and iterative processing outside the data step • Evaluate your programming goals to decide if macros are needed for each program • Start simple and expand to include all parts of macro programming

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