* cvtymdsas.sas Daniel Brockman 070626 Convert yyyymmdd to a SAS date. ;


%macro cvtymdsas(setin, datin, setout, datout) ;
 
/* 
* setin  = the data set on which to operate
* datin  = the name of the variable containing (yy)yymmdd data
* setout = new data set created by this macro.
* datout = the new variable containing SAS date equivalent to 
*          datin and created by this macro.
* 
* This macro incorporates a data step.
* If datin isn't a valid date, then the corresponding value in datout
* will be missing.
* This macro uses three processing variables y, m, and d, which 
* would overwrite any variables by the same names in the setin dataset.
* This macro eliminates all but the first obs for a given date.
*/

%let thisyear = 7;    * we will straightaway overwrite this ; 
%let thiscent = 20;   * we will straightaway overwrite this ;

data NULL (drop=yr);
  yr=year(today()) ;
  call symput('thisyear',yr);   * get the number of the current year;
run;

data &setout (drop=y m d);
  set &setin;

/* There is something wrong with this drop line
  drop y m d ;   * we won't need y m and d after this data step;
*/

  if &datin ;   * keep only obs with date ;

  if (&datin = lag(&datin)) then delete;  * keep only 1st obs with given date ;
  
  * Break date into year, month & day.;
  y = int(&datin/10000);
  m = int((&datin - y*10000)/100);
  d = &datin - y*10000 - m*100 ;

  * convert to yyyymmdd from yymmdd;
  if (y < 100) then do;                   * we have a 2-digit year?;
    y = %eval(%eval(&thisyear/100)*100) + y ; * assume same cent as today;

    if (y < %eval(&thisyear-50)) then do;  * today more than 50 yrs later? ;
      y = 100 + y ;                        * add 100 years to y;
      end;
    else if (y > %eval(&thisyear+50)) then do;  * today > 50 yrs earlier? ;
      y = -100 + y ;                       * subtract 100 years from y;
      end;

    &datin = y * 10000 + m * 100 + d ;     * restate datin;
    end ; * if (y<100) ;

  &datout = input (put (&datin, Z8.), yymmdd8.) ;

run;    * end of data step;

* proc contents data=&setout;   * test;
* run;  * test;

%mend cvtymdsas ;

* ---------------------------------------------------- ;
*/