use strict;
use warnings;

my %hoh;

$hoh{FILENAME1} =
   {
      A => {weight => 3000, intensity => 2},
      B => {weight => 4000, intensity => 3},
   };

$hoh{FILENAME2} =
   {
      C => {weight => 5000, intensity => 3},
      D => {weight => 2000, intensity => 7},
   };

$hoh{FILENAME3} =
   {
      A => {weight => 6000, intensity => 3},
      C => {weight => 1000, intensity => 4},
   };

print
   map
   {
       sprintf qq{weight %d intensity %d Filename %s\n},
          $hoh{$_->[0]}->{$_->[1]}->{weight},
          $hoh{$_->[0]}->{$_->[1]}->{intensity},
          $_->[0];
   }
   sort
   {
       $hoh{$a->[0]}->{$a->[1]}->{weight}
       <=>
       $hoh{$b->[0]}->{$b->[1]}->{weight}
   }
   map
   {
       my $item = $_;
       my @keyPairs;
       push @keyPairs, [$item, $_]
          for keys %{$hoh{$_}};
       @keyPairs;
   }
   keys %hoh;

##</code><code>##

weight 1000 intensity 4 Filename FILENAME3
weight 2000 intensity 7 Filename FILENAME2
weight 3000 intensity 2 Filename FILENAME1
weight 4000 intensity 3 Filename FILENAME1
weight 5000 intensity 3 Filename FILENAME2
weight 6000 intensity 3 Filename FILENAME3