scott bass sas macros

8/3/2019 Scott Bass Sas Macros

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Macro:So What’s Really Going On?

Scott BassSenior ITG Associate

Macquarie Group Services Australia



Agenda

Review of SAS compilation process

What is a macro and what does it do?

Details of SAS compilation process

Macro quoting

Function style macros

My Utility Macro Toolkit



Review...

SAS is a compiled, not interpreted, language

SAS does “just in time” compilation before executing

compiled program

• http://en.wikipedia.org/wiki/Just-in-time_compilation

• http://www.gnu.org/software/dotgnu/libjit-doc/libjit_1.html

Compilation occurs at step boundaries, then compiled code

object is executed. 1

Most novice macro errors I see are timing errors due to alack of understanding of the compiled nature of a SASprogram.

1 See Steven First, Katie Ronk, SUGI 31, Paper 107-31, p. 1 for more details.

http://en.wikipedia.org/wiki/Just-in-time_compilation

http://www.gnu.org/software/dotgnu/libjit-doc/libjit_1.html












Review (cont)...

Four phases in a SAS program compilation:

• Macro compilation

• Macro execution

• SAS code compilation 1

• SAS code execution

1 Technically a PROC step is code parsing, not compilation.

Source: Ian Whitlock, SUGI 30, Paper 252-30, p. 2.



So what is a macro?

A macro is analogous to pre-compiler directives in sayC/C++ (but much more powerful)

http://www.devarticles.com/c/a/Cplusplus/C-plus-plus-Preprocessor-The-Code-in-the-Middle/

“Before the compiler interprets your code, the preprocessor handles it.Its task is to scan through your code and to look for preprocessorinstructions; these can for example be used to replace certaintokens with string or numerical values, or to blank out completesections of the code before the compiler sees it. You can recognize

these instructions from the pound (#) symbol that needs to precedeevery preprocessor instruction.”

“We'll first look at what the preprocessor is used for most: stringsubstitution and conditional compilation.”

Sound familiar?






















So what is a macro? (cont.)

So, a macro...

• Controls the code that gets passed to thecompiler

• Conditional code generation and execution

• Can use SAS data as metadata via the datastep and PROC SQL interfaces, almostalways for use in the next step boundary.

• It is this last point that makes macro so powerful...but also more complex due to timing issues and intermixing of two distinct languages.



How does SAS compile a program?

Input Stack

Word Scanner

• Tokenization (process done by Word Scanner)Macro Processor

SAS Compiler

Source: http://support.sas.com/onlinedoc/913/getDoc/en/mcrolref.hlp/a001071826.htm

http://support.sas.com/onlinedoc/913/getDoc/en/mcrolref.hlp/a001071826.htm






How SAS Processes Statements without Macro Activity





The Macro Processor and Symbol Table



How SAS Processes Statements with Macro Activity





The Macro Processor Examines LET








The Macro Processor Writes to the Symbol Table








The Word Scanner Resumes Tokenization








The Macro Processor Examines &FILE








The Macro Processor Generates Text to the Input Stack

What if the token had been &&FILE&I? (&FILE1=in1, &I=1)








The Word Scanner Completes Processing









Summary:

• Macro processor interacts with the input stack, wordscanner, and symbol table.

• It does not directly interact with the compiler

(indirectly through the input stack).

• It therefore does affect the code seen by the compiler.

• ALL macro processor interaction is TEXT.

o In fact, I tend to think of it as without data type

oYou MUST understand how SAS compiles aprogram, and the timing issues involved, tosuccessfully use macro.



Typical novice error

data two;

set one;

by keyvar;

retain num 0;

if last.keyvar then do;

num+1;

call symputx("mvar"||put(num,best.-L),var);

call symputx("num",num);

end;

if &&mvar&num > 100 then stop;

run;



Macro Quoting

Macro quoting is NOT the same as data step quoting.

• Data step quoting is a directive to the compiler that thistoken is a character constant.

• Macro quoting is the use of macro functions to hidemacro processor directives from the macro processor.

• Non-printing control characters, called deltacharacters, are used to accomplish this. 1

• Sure sign of a macro newbie:%IF “&VAR” = “something” ...

• Need to consider two environments:

oMacro compile time

oMacro execution time

1 Source: http://support.sas.com/onlinedoc/913/getDoc/en/mcrolref.hlp/a001061351.htm





Macro Special Characters

“Macro quoting functions tell the macro processor

to interpret special characters and mnemonics astext rather than as part of the macro language.” 1

Special characters and mnemonics:

1 Source: http://support.sas.com/onlinedoc/913/getDoc/en/mcrolref.hlp/tw3514-overvwqt.htm

blank ) = NE; ( | LE

¬ + # LT

^ -- AND GE

~ * OR GT, (comma) / NOT

' < IN

" > EQ

http://support.sas.com/onlinedoc/913/getDoc/en/mcrolref.hlp/tw3514-overvwqt.htm






Macro Quoting Functions

Summary of Special Characters and Macro Quoting Functions

By Item Group ItemsMacro QuotingFunctions

A + -- */<>=¬^|~;, #blank AND OR NOTEQ NE LE LT GE GT

IN

all

B &% %NRSTR,%NRBQUOTE,%SUPERQ,%NRQUOTE

C unmatched' "() %BQUOTE,%NRBQUOTE,%SUPERQ, %STR*,%NRSTR*,%QUOTE*,%NRQUOTE*






Macro Quoting FunctionsBy Function Affects Groups Works at

%STR A, C* macro compilation

%NRSTR A, B, C* macro compilation

%BQUOTE A, C macro execution

%NRBQUOTE A, B, C macro execution

%SUPERQ A, B, C macro execution (preventsresolution)

%QUOTE A, C* macro execution. Requiresunmatched quotation marksand parentheses to bemarked with a percent sign(%).

%NRQUOTE A, B, C* macro execution. Requiresunmatched quotation marks

and parentheses to bemarked with a percent sign(%).

*Unmatched quotation marks and parentheses must be marked with a percent sign (%)when used with %STR, %NRSTR, %QUOTE, and %NRQUOTE.






Macro Quoting Functions

Mnemonics that help me remember the quoting functions:

• “B” = “batch” macro execution time

• Or simply, %STR and %NRSTR are macrocompilation time, all others are macro execution time

• “NR” = “no resolve” (Item Group B - % &)

Function Mnemonic Masks Timing

%STR Nothing (not B) A, C* Macro compilation

%QUOTE Nothing (not B) A, C* Macro execution(there’s always an exception to the rule!)

%BQUOTE “B” = “batch” A, C Macro execution

%NRSTR Nothing (not B)“NR” = “no resolve”

A, B, C* Macro compilation

%NRQUOTE Nothing (not B)“NR” = “no resolve”

A, B, C* Macro execution(another exception to the rule)

%NRBQUOTE “B” = “batch”

“NR” = “no resolve”

A, B, C Macro execution

%SUPERQ N/A - this one’s just

“Super”!

A, B, C Macro execution (prevents resolution)



Sample Program w/o macro token

%let mvar=A;%let str=%str(A);%let nrstr=%nrstr(A);

%let quote=%quote(A);%let unquote=%unquote(&str);%let example=%nrbquote( 1 + 1 = 3 Today's Test and More );

* continued ... ;




proc sql;select

name, value, value as hexvalue format=$hex8.

from dictionary.macros

wherename in

(“MVAR”,”STR”,”NRSTR”,”QUOTE”,”UNQUOTE”,

”EXAMPLE”)

;

quit; /* See footnote */

Avoids implicit macro variable unquoting: “Some characters in the

above value which were subject to macro quoting have beenunquoted for printing.”

Source: http://www.listserv.uga.edu/cgi-bin/wa?A2=ind0605D&L=sas-l&D=0&P=59246

HUGE thread on macro quoting.

http://www.listserv.uga.edu/cgi-bin/wa?A2=ind0605D&L=sas-l&D=0&P=59246









proc sql;select

name, value

from dictionary.macros

wherename = “A”;quit;

%symdel MVAR STR NRSTR QUOTE UNQUOTE;



Sample Program Results



L-Value vs. R-Value

1 Source: Harry Droogendyk, Marje Fecht, SUGI 31, Paper 251-31, p. 12

References:

• http://en.wikipedia.org/wiki/Value_(computer_science)

• http://www.cutthecrap.biz/software/whitepapers/notanlvalue.html

In simple terms, an R-value is something that can go on the

right side of an equation (equal sign)

“Pure macro”, i.e. code completely resolved by the macro

processor and not sent to the compiler, can generate a R-value. This is much easier with the advent of the %sysfuncfunction.

Known as function-style macros. 1

Changes the “contract” between the calling code and the

called code (macro).

http://en.wikipedia.org/wiki/Value_(computer_science)

http://www.cutthecrap.biz/software/whitepapers/notanlvalue.html








Example L-Value vs. R-Value

L-Value:

%macro nobs_lvalue(data=, mvar=nobs);

%* this is required to use outside the macro ;

%global &mvar;

data _null_;if 0 then set &data nobs=nobs;

call symputx("&mvar",nobs);

stop;

run;

%mend;

%nobs_lvalue(data=sashelp.class,mvar=nobs_lvalue);

%put >>> &nobs_lvalue <<< ;




R-Value:

%macro nobs_rvalue(data=);

%let dsid=%sysfunc(open(&data));

%if (&dsid) %then %do;

%let nobs=%sysfunc(attrn(&dsid,nobs));%let dsid=%sysfunc(close(&dsid));

%end;

%else %do;

%put Unable to open &data;

%let nobs=-1;

%end;

%* Note: no terminating semi-colon! ;

%unquote(&nobs)

%mend;




R-Value:

%let MyMVar=%nobs_rvalue(data=sashelp.zipcode);

%put >>> &MyMVar <<<;

%put %nobs_rvalue(data=sashelp.column);

data _null_;if %nobs_rvalue(data=sashelp.doesnotexist) gt 0

then put "Not empty";

run;

Only a code fragment is returned.

The calling program is responsible for calling the functionstyle macro in a syntactically correct manner.

No need for global macro variable.



My Utility Macro Toolkit

Available for download from the SNUG website are anumber of my utility macros from years of SASprogramming.

My very favourite macros are:

• PARMV – macro parameter validation macro(original author: Tom Hoffman)

• LOOP – loops over a list of tokens calling a child macro foreach token

• SEPLIST – builds a separated list of items

(original author: Richard Devenezia)• NOBS – efficient code to return the number of observations

I also believe the macro header is very well structured andworth a review.



ReferencesGetting Started With Macro , Ian Whitlockhttp://www2.sas.com/proceedings/sugi24/Begtutor/p63-24.pdf

A Serious Look at Macro Quoting , Ian Whitlock (excellent!)http://www2.sas.com/proceedings/sugi28/011-28.pdf

SAS® Macro Design Issues , Ian Whitlock

http://www2.sas.com/proceedings/sugi27/p067-27.pdf

A Second Look at SAS ® Macro Design Issues , Ian Whitlockhttp://www2.sas.com/proceedings/sugi29/244-29.pdf

Macro Bugs – How To Create, Avoid, And Destroy Them ,Ian Whitlock

http://www2.sas.com/proceedings/sugi30/252-30.pdf

http://www2.sas.com/proceedings/sugi24/Begtutor/p63-24.pdf






















References (cont)… Intermediate and Advanced SAS® Macros ,

Steven First, Katie Ronk


Demystifying the SAS® Macro Facility ,Harry Droogendyk, Marje Fecht (excellent!)


Advanced Macro Topics , Steven Firsthttp://www2.sas.com/proceedings/sugi27/p020-27.pdf

Macro Architecture in Pictures , Mark Tabladillo Ph.D.(Object Oriented analysis of SAS Macro – very cerebral but

interesting design ideas)http://www2.sas.com/proceedings/sugi30/168-30.pdf

SAS ® 9.1 Macro Language: Reference (esp. Ch 2)http://support.sas.com/onlinedoc/913/getDoc/en/mcrolref.hlp/a

002293969.htm























References (cont)…Richard Devenezia Website

Excellent source of macros and sample SAS code

http://www.devenezia.com/downloads/sas/macros/index.php

Roland’s SAS Macros

Numerous macros specialized for clinical reportinghttp://www.datasavantconsulting.com/roland/


http://www.datasavantconsulting.com/roland/

http://www.datasavantconsulting.com/roland/




Questions and Contact Details

Scott Bass

Senior ITG Associate

Macquarie Group Services Australia

Email: http://www.linkedin.com/in/scottbass

http://www.linkedin.com/in/scottbass

http://www.linkedin.com/in/scottbass

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