topic Re: delayed resolution in sas macro vars in SAS Programming

delayed resolution in sas macro vars

JMS — Thu, 26 Nov 2015 19:52:54 GMT

With a data step, I can put a macro variable inside another one:

data _null_;
call symput('b','&a');
run;

So &a is now inside b.

Check:

%let a=33;
%put &b;

==> 33
%let a=44;
%put &b;

==> 44

How can I do the same without a datastep, with pure macro programming?

So the code should look like:

%let b= ???(&a);

%let a=33;
%put &b;

%let a=44;
%put &b;

Note that I want to use &b without unquoting. With unquoting it is easy:

%let b=%nrstr(&a);
%let a=33;
%put --- %unquote(&b);
%let a=44;
%put --- %unquote(&b);

But that is not what I want.

Re: delayed resolution in sas macro vars

Patrick — Thu, 26 Nov 2015 19:24:05 GMT

I believe this magic is not possible as a function style macro.

When passing a value to a macro variable which contains an ampersand you must quote the value however you code it.

You could of course wrap your data step into a macro and then call this macro with two parameters.

%macro not_so_magic(l,r);
  %global &l;
  data _null_; 
    call symput("&l",'&'||"&r"); 
  run;
%mend;

%not_so_magic(b,a)
%let a=33; 
%put &=b;
%let a=44; 
%put &=b;

Re: delayed resolution in sas macro vars

FreelanceReinh — Thu, 26 Nov 2015 20:28:34 GMT

What about this?

%let c=%sysfunc(dosubl(data _null_; call symput('b','&a'); run;));
%let a=33; 
%put &b;
%let a=44; 
%put &b;

Ok, it says "%let c=...", not "%let b=...", but what's in a name, after all?

Re: delayed resolution in sas macro vars

JMS — Thu, 26 Nov 2015 20:59:54 GMT

Its not that I need the solution for any project.

I just want to learn about macro and how I can put &a into b.

Re: delayed resolution in sas macro vars

FreelanceReinh — Thu, 26 Nov 2015 21:52:56 GMT

/* Here is a data-step free solution */

%let b=&&%unquote(a);
%let a=33; 
%put &b;
%let a=44; 
%put &b;


/* If you dislike the %UNQUOTE function and know the ASCII table, try this */

%let b=&&%sysfunc(byte(97));
%let a=33; 
%put &b;
%let a=44; 
%put &b;


/* Similar, but showing the "a" in the definition of b: */

%let b=&&%sysfunc(byte(%sysfunc(rank(a))));
%let a=33; 
%put &b;
%let a=44; 
%put &b;


/* Yet another option: */

%let b=&&%sysfunc(cat(a));
%let a=33;
%put &b;
%let a=44;
%put &b;

Re: delayed resolution in sas macro vars

Patrick — Fri, 27 Nov 2015 04:41:36 GMT

@FreelanceReinh

Nice! The doubled ampersand allows you to pass in the ampersand without quoting and after that anything will do that allows to pass in the 'a' without adding a quote to the ampersand but still in a way that the tokenizer doesn't treat it as a macro variable.

Here another option

%let b=&&%left(a);
%let a=33; 
%put b has value: &b;
%let a=44; 
%put b has value: &b;

Re: delayed resolution in sas macro vars

RW9 — Fri, 27 Nov 2015 10:16:20 GMT

The question I wouold ask is why? I find that 99% of tasks can be done in Base SAS. Macro is a utility language to help in generate repeating code and such like, its just a text generator at the end of the day. If I come across a program which has more than one ampersand or percentage in a line, I just delete the program and start again. Have yet to see a valid reason for resorting to macro when re-shaping of data and array/aggregates don't do the same job.

Re: delayed resolution in sas macro vars

JMS — Fri, 27 Nov 2015 16:58:08 GMT

BTW, if you want to look what is "really" in &b, use %superq(b)