my $cnt_unique=0;
for my $row (1 .. $row_max) {
   ... row prep stuff
   for my $col (1 .. $col_max) {
      ... col prep stuff ...
      my $hr = ... your hash for the cell ...

      # Add unique number:
      $hr->{KEY} = $cnt_unique++;

      # Add row & column:
      $hr->{ROW} = $row; $hr->{COL} = $col;
   }
}