order_by_field.php

<?php

$array = array(
    'foo' => 23,
    'bar' => 42,
    'foobar' => 1337
);

$order = array('foo', 'foobar', 'bar');

uksort($array, function($foo, $bar) use($order) {
    return array_search($foo, $fields) > array_search($bar, $fields);
});

var_dump($array);

array(3) {
  ["foo"]=>
  int(23)
  ["foobar"]=>
  int(1337)
  ["bar"]=>
  int(42)
}