Weeks Per Year

There are 24 hours in a day, 7 days in a week and 52 weeks in a year - until there are 53. I have an application that needs to know how many Fridays ( day of week = 6 ) fall in a year. Since 1999 to 2016 the following years have 53 Fridays in a year: 1999, 2004, 2010 and 2016.

The below function will return a value of 52 or 53 as both a custom function and then as a macro function.

proc fcmp outlib = work.functions.utilies ;
  function weeksperyear( weekday, year ) ;
    if year( intnx( 'week.6', nwkdom( 1, weekday, 1, year ), 52 ) ) = year then retval = 53 ;
    else retval = 52 ;
    return ( retval ) ;
  endsub ;
run ;

options cmplib = ( work.functions ) ;

data x ;
  do year = 1992 to 2016 ;
    weeks = weeksperyear( 6, year ) ;
    output ;
  end ;
run ;

/**************************************************************************
*     Program: weeksperyear.sas
*      Author: Tom Bellmer
*     Created: 07NOV2014 
*     Purpose: returns either 52 or 53 weeks
*       Usage: %weeksperyear( weekday = 6, year = 2014 )
*       Notes: weekday= day of the week with 1 = Sun, 2 = Mon ... 7 = Sat
**************************************************************************/

%macro weeksperyear( weekday = 6, year =  2014 ) ;
  %local retval ;

  %if &weekday. eq %then %do ;
    %put %str(E)RROR: Invalid weekday value of &weekday. ;
    %return ;
  %end ;

  %if &year. eq %then %do ;
    %put %str(E)RROR: Invalid year value of &year. ;
    %return ;
  %end ;

  %if %eval( %sysfunc( year( 
               %sysfunc( intnx( week.6
                 , %sysfunc( nwkdom( 1, &weekday., 1, &year. ) )
                 , 52 ) 
               ) 
             ) 
           ) = &year. ) %then %let retval = 53 ;
   %else %let retval = 52 ;

   &retval. 
%mend ;

/* EOF: weeksperyear.sas  */