Get only the array elements with certain keys [duplicate]

Answer 1

You can use FilterIterator

$iterator = new SpecialFilter($items, 'special');
var_dump(iterator_to_array($iterator));

Output

array
  'special_1' => string '3' (length=1)
  'special_2' => string '5' (length=1)
  'special_3' => string '6' (length=1)

Class Used

class SpecialFilter extends FilterIterator {
    private $f;
    public function __construct(array $items, $filter) {
        $object = new ArrayObject( $items );
        $this->f = $filter;
        parent::__construct( $object->getIterator() );
    }
    public function accept() {
        return 0 === strpos( $this->getInnerIterator()->key(), $this->f );
    }
}