introduction to the sas macro facilitypeople.uncw.edu/blumj/advsas/ppt/sas macro facility...

Introduction to the SAS Macro Facility

Uses for SAS Macros

The macro language allows for programs

that are dynamic—capable of self-

modification.

The major components of the macro

language include:

– Macro variables

– Macro statements and functions

– Special programs using some combination of

the above (macros)

An Example

Here is code that will produce summary statistics on mercury level, elevation, surface area and max depth across lake types.

Title 'Summary Statistics';

proc means data=mysas.fish min q1 median q3 max;

class lt;

var hg elv sa z;

run;

quit;

Example (Cont’d)

Suppose I want to generate separate tables for each of the variables listed in the var statement (maybe even delivering each to a separate pdf), what do I have to do?

The macro facility provides a way to execute the same base code under different conditions.

Macro Variables

Macro variables are used to store information that will be used to make code “dynamic”.

All macro variables are character (special functions will be required to do numerical operations).

Macro variables follow the same naming conventions as other variables; however, they are always preceded by an ampersand (&) when referenced.

Revised (yet unsophisticated) Example

%let var=hg;


proc means data=mysas.fish min q1 median q3 max;

class lt;

var &var;

run;

quit;

hg is assigned to the

macro variable var (note,

no ampersand when defined

When the program

runs, the value of

var is substituted

here (ampersand used

during reference)

Assigning Values to Macro Variables

The %let statement can be used to assign

values to macro variables…

– %let is macro statement—all SAS macro

statements (and functions) begin with %.

% and & are referred to as “macro triggers”

– General form %let macro-variable=value

Note: value is not quoted

& is not included in variable name when it is defined

– %let is legal in open code (i.e. outside macros).

What is the Macro Facility Doing?

The macro language’s primary function is as

a text substitution facility and/or code

generator.

To fully understand how macro processing

works, we have to look at how SAS

processes submitted code.

Program Processing and Flow

A SAS program can be any combination of:– Global statements

– Data steps and PROC steps

– Structured Query Language (SQL)

– SAS Component Language (SCL)

– SAS macro language

All submitted programs, regardless of content, are delivered to the input stack.

Compilation and Execution

When the code is delivered to the input

stack, SAS…

– Reads text in the input stack

– Routes text to the appropriate compiler

– Suspends activity when a step boundary is

reached.

– Executes compiled code if there are no errors

– Repeats as necessary.

The Word Scanner--Tokenization

The word scanner breaks up the text into

units known as tokens.

The process (open code):

– The word scanner passes tokens to the

compiler, and the compiler requests tokens until

it receives a semicolon.

– The compiler performs a syntax check on the

statement.

Tokens

There are four types of tokens:

– Literals: Any quoted string

“Any text string” ‘Any text string’

– Numbers: Strings of digits. May include decimal points

and scientific notation

23 23.7 .7 23.7E-10

– Names: Strings of characters beginning with a letter or

underscore

libname _n_ mmddyy10. fred

– Special: Special characters

$ ( ) . & %


proc means data=mysas.fish min median max;

class lt;

var hg;

run;

Compiler

Word Scanner

Input Stack

How many

tokens are

in the first

line of code?

proc

means

data

=

mysas

.

fish

min

median

max

;

class lt;

var hg;

run;

Compiler

Word Scanner

Input Stack

Actually,

the word

scanner

is passing

tokens to

the compiler

at this point



class

lt

;

var hg;

run;

Compiler

Word Scanner

Input Stack

When a

statement is

complete, its

syntax is checked

and it is

compiled



class lt;

var hg;

run;

Compiler

Word Scanner

Input Stack

For procedures

and data steps,

once a step

boundary is

reached, the

compiled code

is executed

Tokenization

How does the compiler know when to execute code?

In an interactive session, is the run statement necessary?

Try submitting the simple program a token at a time (except for proc, which must be submitted with the named procedure).

What Does This Mean for Macros?

Certain tokens are macro triggers…

– % (followed by any name token) is an indication

of a macro statement or function.

– & (followed by any name token) is a reference to

a macro variable.

Let’s look at the following code…

Macro Processing

%let var=hg;



class lt;

var &var;

run;

Compiler

Word Scanner

Input Stack

Macro Processor

Macro Processing

var=hg;



class lt;

var &var;

run;

%let

Compiler

Word Scanner

Input Stack

%let

Macro Processor

The % acts as a macro

trigger. The % and the

following name token

are sent to the macro

processor.

Macro Processing



class lt;

var &var;

run;

var

=

hg

;

Compiler

Word Scanner

Input Stack

%let var=hg;

Macro Processor

The word scanner

will continue to

deliver tokens to

the macro processor

until a semicolon is

reached

%let

Macro Processing



class lt;

var &var;

run;

Compiler

Word Scanner

Input Stack

Macro Processor

%let var=hg;

Variable Value

var hg

Symbol Table

The %let statement

assigns a value to the

macro variable

Macro Processing

;

run;

&var



class lt;

var

Compiler

Word Scanner

Input Stack

Macro Processor

Symbol Table

Remaining statements

up to the var statement

are passed to the compiler.

Variable Value

var hg

Macro Processing

;

run;



class lt;

var

Compiler

Word Scanner

Input Stack

Macro Processor

var

Symbol Table

The & sends var to the

macro processor…

Variable Value

var hg

Macro Processing

hg;

run;



class lt;

var

Compiler

Word Scanner

Input Stack

Macro Processor

var

Symbol Table

Variable Value

var hg

The macro processor

resolves the macro

variable reference and

places the value on the

input stack

Macro Processing



class lt;

var hg;

run;

Compiler

Word Scanner

Input Stack

Macro Processor

Symbol Table

Variable Value

var hg

The remainder of the

code is passed to the

compiler and is

executed

Automatic Macro Variables

By default, SAS has several macro variables

established on its own. These variables

– are created at the invocation of the SAS session

– are global (always available)

– some have been assigned values by SAS (some

are null)

– values can be re-assigned by users in some

cases

Some Automatic Macro Variables

Name Value

SYSDATE Date of SAS invocation (DATE7.)

SYSDATE9 Date of SAS invocation (DATE9.)

SYSDAY Day of the week of SAS invocation

SYSTIME Time of SAS invocation

SYSVER Version of SAS being used

SYSLAST Name of the most recently created data set. If none

have been created, value is _NULL_.

Viewing Macro Variables

The macro language has its own “put”

statement.

Syntax: %put text;

– Writes a new line to the SAS Log

– No quotes are required around text

– Resolves any macro triggers in text

– Can be used in open code

Viewing Automatic Macro Variables

The statement:

Writes names and values of all automatic macro

variables to the Log.

%put _automatic_;

Issues in Resolving Macro Variables

How do each of the following resolve?– %let date=March 14, 1998;

– %let name=John Doe;

– %let value1=3;

– %let value2=4;

– %let sum1=value1+value2;

– %let sum2=&value1+&value2;

Remember, macro variable values are assigned as character strings

Issues in Resolving Macro Variables

Let’s consider a different condition on the

“employees” data set

– Print out selected information for all employees in

a given city.

– The city value should be passed as a macro

variable.

Suppose we try this…

%let city=CARY;

proc print data=mysas.employees noobs;

where upcase(City)=&city;

var EmpID HireDate JobCode City Salary;

run;

What happens?

Resolution of Macro Variables

Though the value of the macro variable city

is stored with the value CARY as text…

– The macro processor passes the value CARY

back to the input stack upon resolving &city

– The token CARY is then passed to the compiler

– Since it is not quoted, it is interpreted by the

compiler as a variable name

– Since there is no variable in the data set called

CARY, an error is generated


A possible solution is to modify the value of

the macro variable:

%let city=‘CARY’;

However, this may not be the best solution,

especially if one wishes to use the token

CARY without the quotes


Another possible solution…%let city=CARY;


where upcase(city)='&city';


run;

?????

Nope…


However, this…%let city=CARY;


where upcase(city)=“&city”;


run;

works!

Important: Every literal is a token, but single quoted strings are not scanned for macro triggers, double quoted strings are.

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