PHP マニュアル: Creates a new set using values that aren't in another set

public Ds\Set Ds\Set::diff(Ds\Set $set)

Creates a new set using values that aren't in another set.

A \ B = {x ∈ A | x ∉ B}

A new set containing all values that were not in the other set.

例1 Ds\Set::diff example

<?php
$a = new \Ds\Set([1, 2, 3]);
$b = new \Ds\Set([3, 4, 5]);

var_dump($a->diff($b));
?>

上の例の出力は、たとえば以下のようになります。

object(Ds\Set)#3 (2) {
  [0]=>
  int(1)
  [1]=>
  int(2)
}