ColumnLength macro function

There are times when you need to dynamically obtain the data type and length of a SAS data set column. This occurred for me when I was writing a generic post process following a proc means with a conditional class statement. I need to know the data type and length of the class variable so that it can be assigned in the ATTRIB statement.

The below code utilizes the %isblank macro function that can be found here. The results of the function will be a dollar sign ($) if it is a character data type followed by the length of the data set column.

The table reveals the various results of calling this macro:

Call	Result	Message
%columnlength(dsn=class, column = age);	8
%columnlength(dsn=class, column = name);	$8
%columnlength(dsn=classx, column = name);		ERROR: The data set classx does not exist.
%columnlength(dsn=class);		ERROR: You must pass in a value for column.
%columnlength(dsn=class, column = namex);		ERROR: Could not find column: namex

Here is an example of how I used this. I have a macro that includes a proc means/summary with a conditional class statement. After the process is finished I want to control the formatting, order and even add a new column. So this is my code snippet

data &dsn;
   attrib
       yyyymm length = $6
   %if not %isblank(&classvar( %then %do;
      &classvar length = %columnlength( dsn = &dsn, column = &classvar)
   %end;
   ...

%macro columnlength( 
     dsn    = 
   , column = 
);

   %local
      dsid
      position
      type
      retval
   ;

   %if not %sysfunc(exist(&dsn)) %then %do;
      %put %str(E)RROR: The data set &dsn does not exist.;
      %return;
   %end;

   %if %isblank(&column) %then %do;
      %put %str(E)RROR: You must pass in a value for column.;
      %return;
   %end;

   %let dsid = %sysfunc(open(&dsn.));
   %if &dsid %then %do;
      %let position = %sysfunc(varnum(&dsid, &column));
      %if &position = 0 %then %put %str(E)RROR: Could not find column: &column.;
      %else %do;
         %if %sysfunc(vartype(&dsid, &position)) = C %then %let type = $;
         %let retval = &type%sysfunc(varlen(&dsid, &position));
      %end;
      %let dsid = %sysfunc(close(&dsid));
   %end;

   &retval
%mend;