Hi again,

Maybe this rudimentary implementation will help:

use strict;
use warnings;
use feature 'say';

my %data;

for (0..14) {
    my ($lpn, $ppn, $cnt_subppn) = get_ns();
    push @{ $data{$lpn}{$ppn} }, (0..$cnt_subppn);
}

for my $lpn ( sort {$a <=> $b} keys %data ) {
    say "$lpn:";
    for my $ppn ( sort {$a <=> $b} keys %{ $data{$lpn} } ) {
        say "  $ppn:";
        for my $sub_ppn ( sort {$a <=> $b} @{ $data{$lpn}{$ppn} } ) {
            say "    $sub_ppn";
        }
    }
}


sub get_ns {
    return (int(rand(10)), int(rand(10)), int(rand(10)));
}
[download]

Note adds multiple entries for the same "sub_ppn"; you could count instead.

Example output:

0:
  7:
    0
    1
    2
    3
    4
    5
    6
    7
    8
    9
2:
  2:
    0
    1
    2
  9:
    0
    1
    2
    3
    4
3:
  5:
    0
    1
    2
    3
  8:
    0
    1
    2
    3
    4
    5
    6
    7
    8
4:
  3:
    0
    1
    2
    3
    4
    5
    6
    7
    8
  7:
    0
    1
  9:
    0
    1
    2
5:
  2:
    0
    1
    2
    3
    4
    5
6:
  8:
    0
    0
    1
    1
    2
    2
    3
    3
    4
    4
    5
    6
    7
    8
    9
  9:
    0
    1
    2
    3
    4
    5
    6
    7
    8
7:
  7:
    0
    1
    2
    3
    4
    5
    6
    7
8:
  4:
    0
    1
    2
    3
    4
    5
    6
9:
  3:
    0
    1
[download]

Hope this helps!