perl到php的翻译

如何将此perl子例程转换为PHP函数

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) ;
}

我这里有个问题：

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

变成

foreach ($aggregate as $key => $cat_a)

---

假设$aggregate是一个关联数组。

AFAIK，PHP中的所有数组都是关联的。在这个表达式中“&”的用途是什么：“…*&$distance\u metric（$cat\u a，$cat\u b）}”？

// &$... is a value reference instead of a value copy, when in doubt use $...
foreach ($aggregate as $cat_a => &$val_a) {
  foreach ($aggregate as $cat_b => &$val_b) {
    if ($cat_a !== $cat_b) $disagreement += $val_a * $val_b ...;
  }
}

// &$... is a value reference instead of a value copy, when in doubt use $...
foreach ($aggregate as $cat_a => &$val_a) {
  foreach ($aggregate as $cat_b => &$val_b) {
    if ($cat_a !== $cat_b) $disagreement += $val_a * $val_b ...;
  }
}