Why Use Macros

8/8/2019 Why Use Macros

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INTRODUCTION

The SAS Macro Language allows you

to extend and customize the SAS System

to simplify large programs

to reduce the amount of text you enter

to invoke code several times

to minimize the mistakes you might make

The macro language is a powerful additionto SAS, allowing increased efficiency and

customization of SAS jobs


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INTRODUCTION

Macro programming is generally

considered an advanced topic

But, while macros certainly can bechallenging, it is also true that the basic

concepts are not difficult to learn


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INTRODUCTION

This course is designed for students

who know the basics of SAS

programming, but know nothing aboutSAS macro programming

As we wont start from the very

beginning, if you are not a SAS user at

all, then it is not a course for you


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INTRODUCTION

We explain

how the macro processor works, and

how to use macros and macro variables Using these techniques you can create

flexible, reusable code that can save

you time and effort


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INTRODUCTION

Because macro code takes longer to

write and debug than standard SAS

code, you generally wont use macrosin programs that will be run only a few

times

But if you find yourself writing similar

code over and over again, then macros

may make your job easier


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MACROS CAN HELP

First, with macros you can make one small

change in your program and have SAS echo

that change throughout your program

Second, macros can allow you to write a

piece of code and use it over and over again

in the same program or in different programs

Third, you can make your programs datadriven, letting SAS decide what to do based

on actual data values


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The most important concept to keep in

mind whenever you write macro code

is that

THE MACRO PROCESSOR

macro

statementsstandard

SAS statements

macro

processor

You are writing a program

that writes a program


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INTRODUCTION

When you submit a standard SAS

program, SAS compiles and then

immediately executes it But when you write macrocode, there

is an extra step


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INTRODUCTION

Before SAS can compile and execute

your program, SAS must pass your

macro statements to the macroprocessor which then resolves your

macros generating standard SAS code

Because you are writing a program that

writes a program, this is sometimes

called meta-programming


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Lets do exercises

Scenario

25 data sets with one same variable named

TEMP for year 1981 2006

YR1981, YR1982, . , and YR2006

Find mean TEMP for each year

PROC MEANS DATA=yr1981;

VAR temp;

RUN;


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INTRODUCTION

The SAS macro language consists of

macro variables,

macro programs, macro facility interfaces, and

macro storage techniques


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MACRO VARIABLES

SAS macro variables are the basic units that

are used by macro facility interfaces and

macro programs

They can be created and resolved anywhere

in a SAS program

The name and value of a macro variable is

stored in memory in a Symbol Table, eitherlocal or global in scope; the value is always

simply a string of characters


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MACRO VARIABLES

Macro variables come in two varieties: eitherlocal or global

A macro variables scope is local if it is

defined inside a macro Its scope is global if it is defined in open

code which is everything outside a macro.

You can use a global macro variable

anywhere in your program, but you can usea local macro variable only inside its ownmacro.


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MACRO VARIABLES

If you keep this in mind as you write

your programs, you will avoid two

common mistakes: trying to use a local macro variable

outside its own macro, and

accidentally creating local and global

macro variables having the same name


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MACROS vs. MACRO

VARIABLES

A macro variable is like a standard

data variable except that it does not

belong to a data set and has only asingle value which is always character

The value of a macro variable could be

a variable name, a numeral, or any text

you want substituted in your program


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MACROS vs. MACRO

VARIABLES

The names of macro variables start with anampersand (&), while the names of macrosstart with a percent sign (%)

The % and & characters are called macrotriggers; the character following the macrotrigger must not be a space

%let dset = MASTER ;PROC PRINT DATA=&dset ;

RUN;


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USER-DEFINED MACRO

VARIABLES

the %LET statement enables you to define a

macro variable and assign it a value %LETvariable = value ;

length range is 0-32K characters

mathematical expressions are not evaluated

leading and trailing blanks are removed from

value before the assignment is made

if variable already exists, value replaces thecurrent value


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SYSTEM-DEFINED MACRO

VARIABLES

System-defined macro variables are

created by the SAS Supervisor

created at SAS invocation are global(always available)

can be assigned values by the user in

some cases


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VARIABLES

some system-defined macro variables

NAME VALUE

SYSDATE date of SAS invocation

SYSDAY day of the week of SAS invocation

SYSTIME time of SAS invocation

SYSSCP operation system being used

SYSVER release of SAS system being used

SYSERR return code set by last DATA or PROC step

SYSLAST name of most recently created SAS data set in the form oflibref.name. If no data set was created then the value is

_NULL_ .


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VARIABLES

NOTE: the value of macro variables

SYSDATE and SYSTIME are character

strings, not SAS date or time values. Example:

%let job = HW1 ;

Footnote "&job by YUFEN LI on

&SYSDATE &SYSTIME";

Footnote " HW1 by YUFEN LI on 06NOV06 18:45 "


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MACRO PROGRAMS

similar to a subroutine or function in a

procedural programming language e.g.

Fortran, C/C+/C++

with a name which is used to call it,

and it can accept parameters

the names of macros start with apercent sign (%)


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MACRO PROGRAMS

Syntax

%MACRO macro-name (parameters);

macro-text

%MEND macro-name;

parameters are separated by commas

there are two type of macro parameters:positional and keyword


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TYPE OF MACRO

PARAMET

ERS positional parameters receive their values in the

order (position) in which they are specified in themacro invocation positional parameters, if any, must appear first in the

parameter list

keyword parameters are those which start with thename of the macro variable followed by an = symboland optionally followed by an initial value keyword parameters may appear in any order after

positional parameters%macro means(procopt,vars,dsn=_last_) ;

proc means &procopt data = &dsn;

var &vars ;

%mend means;


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MORE FLEXIBILITIES

The following macro definition has onepositional parameteropts (with no = sign)and one keyword parameterfilenm (with an

= sign)

%macro mname (opts,filenm=file5);

proc print data=&filenm &opts;

title " Print &filenm data ";run;

%mend;


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MORE FLEXIBILITIES

This macro can be called with any of

these formats, specifying either or both

or neither of the parameters:

%mname ()

%mname (double)

%mname (filenm=file6)

%mname (double noobs, filenm=file7)


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MACRO PROGRAMS

Example%macro mname;

proc print data=data.all;

where var1=&newvalue;title " Print &syslast data ";

run;

%mend;

OPTIONS MPRINT MLOGIC;

%let newvalue=17;

%mname


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MACRO PROGRAMS

Notice that there is NO SEMICOLON after%mname

This line calls the macro named mname;

there is no semicolon there because that linewill be replaced by the code from the macroprogram itself, which has the requiredsemicolons

Specify the MPRINT and MLOGIC options togenerate as much information as possiblefrom the macro processor


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OPTION MPRINT

You can see that SAS has inserted into the

regular SAS log the MPRINT lines

The statements generated by the macro

processor are all labeled with the word

MPRINT followed by the name of the macro

that generated the statements

By using the MPRINT system option it iseasy to see the standard SAS statements

your macro is generating


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OPTION MLOGIC

Use MLOGIC to debug macros

If MLOGIC is in effect and the macroprocessor encounters a macro invocation,

the macro processor displays messages thatidentify the beginning of macro execution

the values of macro parameters at that point

the execution of each macro program statement whether each %IF condition is true or false

each iteration of the %DO loop

the end of macro execution


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MACRO FACILITY

INTERFACES

Macro Facility Interfaces are ways to

use macro variables. They are :

1) CALL SYMPUT (macro-variable, text);This creates a macro variable named

macrovariable with a value of text.


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MACRO FACILITY

INTERFACES

2) Indirect References using multipleampersands. A double ampersand (&&) inSAS code is resolved to a single ampersand

If we have a macro variable var1 with avalue of char1, and another macro variablechar1 with a value of Taiwan, then a string

in the SAS code of &&&var1 is resolved to&char1 on the first pass, and that isresolved to Taiwan on the second pass


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MACRO FACILITY

INTERFACES

3) PROC SQL; SELECT INTO :macrovariable;

proc sql;

select sum(amount) into:total from data.overall;

run;

This defines a macro variable total with a

value that is the string representing the sum of

variable amount in SAS data set data.overall


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STORAGE TECHNIQUES

There are three ways to store macro programsfor future use:

1. Store the source code in an external file

and use this statement to pull it into a SASprogram:

%include(file-pathname);

2. Use the Autocall Facility to searchpredefined source libraries for macrodefinitions. These libraries can consist ofexternal files or SAS catalogs.


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STORAGE TECHNIQUES

3. Store the compiled macros. This does NOTsave the SOURCE code. Always maintainthe source code separately

To store the compiled macro :libname dlib library-path;

options mstored sasmstore=dlib;

%macro mname(parameters) / store

des=description;

%mend;

To access this stored macro :libname dlib library-path;

options mstored sasmstore=dlib;

%mname(parameters)


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In-Class Assignment

Write a SAS macro program to provide the

solutions of aX2 + bX + c = 0 for varied a, b,

and c

What expected to see in the OUTPUT is

Question Solution1 Solution2

X2 + 4X + 4 = 0 -2 -2

X2 + 5X + 4 = 0 -1 -4

X2 - 5X + 4 = 0 4 1


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In-Class Assignment

1. Start with a general SAS code to print

out the solutions of X2 + 4X + 4 = 0

2. Convert the previous code as amacro program with three parameters

to take values of a, b, and c

3. Celebrate with your first macro code

Why Use Macros

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