my $AoH = [ { page => 'main',
              chap => 'About'},
            { page => 'main',
              chap => 'Contact'},
            { page => 'main',
              chap => 'About'},
            { page => 'sub',
              chap => 'About'},
            { page => 'sub',
              chap => 'Contact'}
          ];

my %uniq = map { ($_->{page} => 1, $_->{chap} => 1) } @$AoH;
@$AoH = map { { page => $_ , chap=>$_ } } keys %uniq;

print Dumper ($AoH);

##</code><code>##

$VAR1 = [
          {
            'chap' => 'Contact',
            'page' => 'Contact'
          },
          {
            'chap' => 'About',
            'page' => 'About'
          },
          {
            'chap' => 'sub',
            'page' => 'sub'
          },
          {
            'chap' => 'main',
            'page' => 'main'
          }
        ];

##</code><code>##

$VAR1 = [
          {
            'page' => 'main',
            'chap' => 'About'
          },
          {
            'page' => 'main',
            'chap' => 'Contact'
          },
          {
            'page' => 'sub',
            'chap' => 'About'
          },
          {
            'page' => 'sub',
            'chap' => 'Contact'
          }
        ];

##</code><code>##

   'page' => 'main',
   'chap' => 'About'