- data a;
- input code firm $ year1 year2;
- cards;
- 1 a 2006 2004
- 2 b 2005 2004
- ;
- run;
- data b;
- set a;
- do year=min(year1,year2) to max(year1,year2) by 1;
- output;
- end;
- drop year1 year2;
- run;
- proc sort data=b;
- by code firm year;
- run;
- data c;
- set b;
- by code firm year;
- if last.code then var=1;
- else var=0;
- run;