Description:
------------
You can see all information in the test script.

Test script:
---------------
$inputArray = array(
	'shipping' => array(
		'after' => array(),
		'before' => array(),
		'_code' => 'shipping'
	),
	'freeshipping' => array(
		'after' => array(),
		'before' => array(),
		'_code' => 'freeshipping'
	),
	'discount' => array(
		'after' => array('shipping', 'tax_shipping'),
		'before' => array(),
		'_code' => 'discount'
	),
	'tax_shipping' => array(
		'after' => array('shipping'),
		'before' => array('discount'),
		'_code' => 'tax_shipping'
	)
);

function compare ($a, $b) {
	$aCode = $a['_code'];
	$bCode = $b['_code'];
	if (in_array($aCode, $b['after']) || in_array($bCode, $a['before'])) {
		$res = -1;
	} elseif (in_array($bCode, $a['after']) || in_array($aCode, $b['before'])) {
		$res = 1;
	} else {
		$res = 0;
	}
	return $res;
}

uasort($inputArray, 'compare');
var_dump(array_keys($inputArray));

Expected result:
----------------
array (size=4)
  0 => string 'shipping' (length=8)
  1 => string 'tax_shipping' (length=12)
  2 => string 'discount' (length=8)
  3 => string 'freeshipping' (length=12)

Or another position for 'freeshipping'. But 'shipping' must be before 'tax_shipping' and 'discount' must be after 'tax_shipping'.

Actual result:
--------------
array (size=4)
  0 => string 'tax_shipping' (length=12)
  1 => string 'discount' (length=8)
  2 => string 'freeshipping' (length=12)
  3 => string 'shipping' (length=8)