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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 - PowerPoint PPT Presentation
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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