use v5.12;
use warnings;
use Data::Dump;


my $AoH;

debug_loop_join();exit;

sub loop_join {
    my %H;
    $H{$_} = ()  for @$AoH;
    return keys %H;
}
sub debug_loop_join {
    $AoH = create_data (.2, 10);
    ddx [ loop_join  ($AoH) ];
    ddx [ sort  loop_join  ($AoH) ];
    ddx [ sort {$a cmp $b } loop_join  ($AoH) ];
}


sub create_data {
    my ($density, $records) = @_;

    my @AoH;
    push @AoH, {map { rand 100 <= $density ? ( $_ => $_ ) : () } "A" .. "ZZ"}
        for 1 .. $records;
    return \@AoH;
}