SAS: MACROSComputing for Research I

Spring 2014January 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 Dynamically create code at execution

time

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

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

The SAS Macro Facility

Macro statements

Macro processor

Standard SAS statements

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

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

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

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

Macro Variables: System

SYSCMD LAST NON-SAS COMMAND ENTEREDSYSDATE CURRENT DATE IN DATE6. OR DATE7. FORMATSYSDAY CURRENT DAY OF THE WEEKSYSDEVIC CURRENT GRAPHICS DEVICESYSDSN LAST SAS DATASET BUILTSYSINDEX NUMBER OF MACROS STARTED IN JOBSYSINFO SYSTEM INFORMATION GIVEN BY SOME PROCSSYSPROD INDICATES WHETHER A SAS PRODUCT IS

LICENSEDSYSSCP OPERATING SYSTEM WHERE SAS IS RUNNINGSYSTIME STARTING TIME OF JOBSYSVER SAS VERSION

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 21JAN14AUTOMATIC SYSDATE9 21JAN2014AUTOMATIC SYSDAY TuesdayAUTOMATIC SYSTIME 17:45AUTOMATIC SYSVER 9.2

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 an

ampersand (&) 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

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.

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

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

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

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

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

Macro Variable Resolution Examples of the use of delimiters for

macro variables in text %let var1=final; %let var2=exam;

Syntax ResultTitle “This is the &var1&var2”; This is the finalexam

Title “This is the &var1..”; This is the final.

Title “This is the &var1. &var2..”;

This is the final exam.

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.

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: proc sql; 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)

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;

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

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

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

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:

proc freq data=grades; where gender=“Male” and sport=“Football”; table grades; title “Grade Distribution for Male Football Players”; run;

Macro Example Define the macro syntax:

%macro grade(gender=,sport=); proc freq 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)

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”;proc gplot 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

Macro Example 2 Macro Syntax:

%macro doses (cohort=,dose=,num=);title “Cohort &cohort., Dose Level &dose. Over Time”;proc gplot 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)

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

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

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

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; var inr creatinine; run; quit;%MEND report;

%report(injurytype=severe)%report(injurytype=mild)

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

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

%macro subs;

proc sql; 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

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