# compare ordered date strings
     my $result = sprintf("%04d%02d%02d",@date_1[2,0,1])
                  <=>
                  sprintf("%04d%02d%02d",@date_2[2,0,1]);

     # $result is -1, 0 or 1, so amend for output
     # to return only 0 or 1;
     return ($result + $result**2)/2;
[download]

Hmm... That's a neat trick with exponentiation to convert -1 to 0, but wouldn't this be much simpler?

# compare ordered date strings
return sprintf("%04d%02d%02d",@date_1[2,0,1])
       >
       sprintf("%04d%02d%02d",@date_2[2,0,1]);
[download]