# supporting constants:
my %fnum = { 'region' => 0, 'date' => 1, 'type' => 2, 'channel' => 3 };
my $fsize = 4;

sub reduce {
  my ($dc,$f) = @_;
  # sort fields to keep in decending order
  my @keep = reverse sort map { $fnum{$_} } @$f;
  
  for $cnt ($fsize-1 .. 0) {
    # hard code goes here! lol
  }
}