my @subfields = qw( REQ POS LENGTH data FILTER );
my @sorted_keys = sort qw( field1 field2 );
my @mydata = ( [ 'Y', 34, 10, ' ' x 10, \&default_filter ],
               [ 'Y', 35, 10, ' ' x 10, \&default_filter ] );
my $type = 'that_type';
for my $k (@sorted_keys) {
  @{ $hash{$type}{$k} }{ @subfields } = @{ shift @mydata };
}