Nasıl bu perl yordam bir PHP fonksiyonu haline çevirmek?

sub disagreement {
  my $disagreement = 0;
  my %aggregate = () ;
  foreach my $item (@_) {$aggregate{$item}++}
  foreach my $cat_a (keys %aggregate) {
    foreach my $cat_b (keys %aggregate) {
      if ($cat_a != $cat_b) {$disagreement += $aggregate{$cat_a} * $aggregate{$cat_b} * &$distance_metric ($cat_a , $cat_b)}
    }
  }
  $disagreement /= @_ * (@_ - 1) ;
  return ($disagreement) ;
}

Burada bir sorun var:

foreach my $cat_a (keys %aggregate) {
    foreach my $cat_b (keys %aggregate) {
    }
}