@firstcol = map { $$_[0]  } @$data;
@numbers = (1) x scalar(@firstcol); # init to (1,1,1,...)

for ($i = $#firstcol; $i > 0; $i--) {
        if ($firstcol[$i] eq $firstcol[$i-1]) {
                $numbers[$i-1] = $numbers[$i]+1;
                $numbers[$i] = 0;
        }
}