sub commonLists {
    my ( $array_ref1, $array_ref2, $elementToMatch ) = @_;

    my %lookup = map { $_->[$elementToMatch] => $_ } @$array_ref1;

    my @match;
    foreach my $fromArray2 (@$array_ref2) {
        my $fromArray1 = $lookup{$fromArray2->[$elementToMatch]};
        push(@match, $fromArray1, $fromArray2) if $fromArray1;
    }
    return \@match;
}

##</code><code>##

sub commonLists {
    my ( $array_ref1, $array_ref2, $elementToMatch ) = @_;

    my %lookup;
    push(@{$lookup{$_->[$elementToMatch]}}, $_)
       foreach @$array_ref1;

    my @match;
    foreach my $fromArray2 (@$array_ref2) {
        my $fromArray1 = $lookup{$fromArray2->[$elementToMatch]};
        push(@match, @$fromArray1, $fromArray2) if $fromArray1;
    }
    return \@match;
}