Hi, here's one way*:

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

my %keep;
for my $line ( <DATA> ) {
    chomp $line;
    my ( $P1, $P2, $I ) = split /,/, $line;
    $keep{"$P1$P2"} = $line;
    if ( $keep{"$P2$P1"} ) {
        delete $keep{"$P2$P1"};
        delete $keep{"$P1$P2"};
    }
}

say for values %keep;

__DATA__
personG,personH,42
personA,personB,10
personB,personA,190
personA,personC,23
personA,personD,43
personE,personF,10
[download]

Output:

$ perl 1226286.pl

personG,personH,42
personE,personF,10
personA,personD,43
personA,personC,23
[download]

... add sorting etc. as you wish ...

Hope this helps!

(*Disclaimer: pre-coffee!)