How to conditionally execute SAS global statements

March 15, 2021
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SAS global statementsSAS global statements define certain SAS objects and set values for system options. They take effect as soon as SAS compiles programming statements and persist during the entire SAS session or until another global statement overrides them. They can be used in open code, within macros, as well as within DATA and PROC steps. Here are the most used global statements:

  • FILENAME statement
  • LIBNAME statement
  • OPTIONS statement
  • TITLE statement
  • FOOTNOTE statement
  • X statement

NOTE: In SAS Viya, global statements are not supported on the CAS server.

Real meaning of “global statements are not executable”

I know, the title of this blog post may sound like an oxymoron. Even though SAS global statements can appear in DATA steps, they are not executable by definition. They are so not executable, that they even syntactically cannot be a part of the IF-THEN/ELSE statement that executes DATA step statements depending on specified conditions:

IF expression THEN executable-statement1;
<ELSE executable-statement2;>

Try sticking it in there and SAS will slap you with an ERROR:

data _null_;
   set SASHELP.CARS nobs=n;
   if n=0 then libname outlib 'c:\temp';
run;

SAS log will show:

3       if n=0 then libname outlib 'c:\temp';
                    -------
                    180
ERROR 180-322: Statement is not valid or it is used out of proper order.

But global statements’ “not executable” status only means that they cannot be executed as part of a DATA step execution. Otherwise, “they take effect” (in my mind that equates to “they execute”) right after the compilation phase but before DATA step executes (or processes) its data reads, writes, logic and iterations.

Here is another illustration. Let’s get a little creative and tack a LIBNAME global statement within conditionally executed DO-group of the IF-THEN statement:

data OUTLIB.CARS;
   set SASHELP.CARS nobs=n;
   if n=0 then
   do;
      libname OUTLIB 'c:\temp';
   end;
run;
 
In this case, SAS log will show:
NOTE: Libref OUTLIB was successfully assigned as follows:
      Engine:        V9
      Physical Name: c:\temp
NOTE: There were 428 observations read from the data set SASHELP.CARS.
NOTE: The data set OUTLIB.CARS has 428 observations and 15 variables.

As you can see, not only our LIBNAME statement “executed” (or “took effect”) despite the IF-THEN condition was FALSE, it successfully assigned the OUTLIB library and applied it to the data OUTLIB.CARS; statement that appears earlier in the code. That is because the LIBNAME global statement took effect (executed) right after the DATA step compilation before its execution.

For the same reason, you can place global statement TITLE either in open code before PROC that produces output with a title or within that PROC. In the first case, the stand-alone TITLE statement is compiled on its own and immediately executed thus setting the title for the PROCs that follow. In the latter case, it is compiled with the PROC step, then immediately executed before PROC step’s execution.

Now, when we have a solid grasp of the global statements timing habits, let’s look at the coding techniques allowing us to take full control of when and whether global statements take effect (executed).

Macro language to conditionally execute SAS global statements

Since SAS Macro processor acts before SAS language compiler, we can conditionally generate SAS global statements using SAS macro language. These macro-generated global statements are then injected into SAS code passed on to the SAS compiler. SAS compiler receives these conditionally generated global statements and executes them accordingly.

Here is a code example:

%let dsname = SASHELP.CARS;
/*%let dsname = SASHELP.CLASS;*/
 
%let name = %scan(&dsname,2);
 
%if (&name eq CARS) or (&name eq CLASS) %then
%do;
   options DLCREATEDIR;
   libname outlib "c:\temp\&name";
%end;
%else
%do;
   libname outlib "c:\temp";
%end;
 
data OUTLIB.&name;
   set &dsname;
run;

In this code, if name is either CARS or CLASS the following global statements will be generated and passed on to the SAS compiler:

   options DLCREATEDIR;
   libname outlib "c:\temp\&name";

This will create a directory c:\temp\&name (if it does not exist) and assign libref OUTLIB to that directory.

Otherwise, the following global statement will be generated and passed on to the SAS compiler:

   libname outlib "c:\temp";

The DATA step then creates data set OUTLIB.&name in the corresponding dynamically assigned library. Using this technique, you can conditionally generate global statements for SAS system options, librefs, filerefs, titles, footnotes, etc. SAS compiler will pick up those generated global statements and execute (activate, put in effect) them.

CALL EXECUTE to conditionally execute SAS global statements

Sometimes, it is necessary to conditionally execute global statements based on values contained in data, whether in raw data or SAS data sets. Such a data-driven approach can be easily implemented using CALL EXECUTE routine in a DATA step. CALL EXECUTE routine resolves its argument and issues the resolved value for execution after a step boundary.

For example, suppose we want to produce separate report listings for each car make in SASHELP.CARS data set. We want titles of these listings to individually identify each car make.

Here is how this can be done:

data _null_;
   set SASHELP.CARS;
   by MAKE;
   if first.MAKE then
   do;
      call execute('title "'||trim(MAKE)||' models";');
      call execute('proc print noobs data=SASHELP.CARS(where=(MAKE="'||trim(MAKE)||'"));');
      call execute('   var MAKE MODEL TYPE;');
      call execute('run;');
   end;
run;

In this code, for every block of unique MAKE values (identified by first.MAKE) we have CALL EXECUTE generating lines of SAS code and pushing them outside the DATA step boundary where they compile and execute. The code snippets for TITLE and WHERE clause are data-driven and generated dynamically. The SAS log will show a series of the generated statements:

NOTE: CALL EXECUTE generated line.
1   + title "Acura models";
2   + proc print noobs data=SASHELP.CARS(where=(MAKE="Acura"));
3   +    var MAKE MODEL TYPE;
4   + run;
 
5   + title "Audi models";
6   + proc print noobs data=SASHELP.CARS(where=(MAKE="Audi"));
7   +    var MAKE MODEL TYPE;
8   + run;

. . . and so forth.

In this implementation, global statement TITLE is prepared (“pre-cooked”) conditionally (if first.MAKE is TRUE) within the DATA step in a form of a character value. It’s still not a global statement until CALL EXECUTE pushes it out of the DATA step. There it becomes a global statement as part of SAS code stream. There it gets compiled and executed, setting a nice data-driven title for the PROC PRINT output (individually for each Make):

PROC PRINT outputs with dynamically generated titles

Additional resources

Your thoughts?

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How to conditionally execute SAS global statements was published on SAS Users.

This post was kindly contributed by SAS Users - go there to comment and to read the full post.

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