How to extract key=>value pairs from this array

I have this array

[InstrumentCategory] => Array
                (
                    [0] => Array
                        (
                            [id] => 4
                            [title] => Training
                            [InstrumentsCategory] => Array
                                (
                                    [id] => 56
                                    [instrument_id] => 28
                                    [category_id] => 4
                                )

                        )

                    [1] => Array
                        (
                            [id] => 8
                            [title] => Working time flexibility
                            [InstrumentsCategory] => Array
                                (
                                    [id] => 57
                                    [instrument_id] => 28
                                    [category_id] => 8
                                )

                        )

                    [2] => Array
                        (
                            [id] => 16
                            [title] => Income support for workers
                            [InstrumentsCategory] => Array
                                (
                                    [id] => 55
                                    [instrument_id] => 28
                                    [category_id] => 16
                                )

                        )

             开发者_JAVA百科   )

Is there any other way to extract id=>value pairs (note that id in this case is a key in the sub-arrays) than a for loop?

Thanks in advance

---

If you use PHP 5.3, you can use the following code (array_reduce):

$r = array_reduce($input_array,
                  function ($res, $cur) {
                      return $res + array($cur['id'] => $cur);
                  }, array());

Afterwards, $r contains id => value pairs.

Edit: With a PHP version < 5.3, you can do the following:

function array_reduce_cb_id ($res, $cur) {
    return $res + array($cur['id'] => $cur);
}

$r = array_reduce($input_array, 'array_reduce_cb_id', array());