use strict;
use warnings;

my %hoh = (
        FILENAME1 => {
            A => {weight => 3000, intensity => 2},
            B => {weight => 4000, intensity => 3},
        },
        FILENAME2 => {
            D => {weight => 2000, intensity => 7},
            C => {weight => 5000, intensity => 3},
        },
        FILENAME3 => {
            C => {weight => 1000, intensity => 4},
            A => {weight => 6000, intensity => 3},
        },
    );

my @lines = map {$_->[1]} sort {$a->[0] <=> $b->[0]} map {
        my $fn = $_;
        map {
            my $h = $hoh{$fn}{$_};
            [$h->{weight}, "$fn $_ $h->{intensity}: $h->{weight}"]
        } keys %{$hoh{$fn}}
    } keys %hoh;

print join "\n", @lines;