Pinq\ITraversable::groupBy PHP Метод

    public function groupBy(callable $function);

 /**
  * @dataProvider assocOneToTen
  */
 public function testThatGroupByGroupsTheElementsCorrectlyAndPreservesKeys(\Pinq\ITraversable $traversable, array $data)
 {
     $isEven = function ($i) {
         return $i % 2 === 0;
     };
     //First number is odd, so the first group should be the odd group
     list($odd, $even) = $traversable->groupBy($isEven)->asArray();
     $this->assertMatches($odd, array_filter($data, function ($i) use($isEven) {
         return !$isEven($i);
     }));
     $this->assertMatches($even, array_filter($data, $isEven));
 }