如何对从API调用返回的simplexml进行排序

Question

我需要对这个多维数组进行排序，而我在本网站或通过我的朋友Google找到的任何内容都没有让我找到正确的解决方案。

$url = file_get_contents('http://api.petfinder.com/shelter.getPets?key=&id=&status=A&output=full&count=999');
$xml = simplexml_load_string($url); 
// this is the returned array (see below for example)

foreach($xml->pets->pet as $pet) { 
// ->pet, or $pet is what needs to be sorted
    $data['id'] = (string)$pet->id;
}

以上是API调用返回的数组示例...

SimpleXMLElement Object
(
[header] => SimpleXMLElement Object
    (
        [status] => SimpleXMLElement Object
            (
                [code] => 100
            )
    )
[lastOffset] => 82
[pets] => SimpleXMLElement Object
    (
        [pet] => Array
            (
                [0] => SimpleXMLElement Object
                    (
                        [id] => 10595710
                        [name] => Lizzie
                        [animal] => Dog
                        [options] => SimpleXMLElement Object
                            (
                                [option] => Array
                                    (
                                        [0] => altered
                                        [1] => hasShots
                                        [2] => housebroken
                                    )
                            )
                        [lastUpdate] => 2012-10-11T15:19:05Z
                        [media] => SimpleXMLElement Object
                            (
                                [photos] => SimpleXMLElement Object
                                    (
                                        [photo] => Array
                                            (
                                                [0] => http://photos.petfinder.com/photos/US/NC/NC416/10595710/NC416.10595710-1-x.jpg
                                                [1] => http://photos.petfinder.com/photos/US/NC/NC416/10595710/NC416.10595710-1-fpm.jpg
                                            )
                                    )
                            )
                        [contact] => SimpleXMLElement Object
                            (
                                [email] => jghfjhgf
                            )
                    )
                [1] => SimpleXMLElement Object
                    (
                        [id] => 11036032
                        [name] => Buddy
                        [animal] => Dog
                        [breeds] => SimpleXMLElement Object
                            (
                                [breed] => Array
                                    (
                                        [0] => Terrier
                                        [1] => Black Labrador Retriever
                                    )

                            )
                        [options] => SimpleXMLElement Object
                            (
                                [option] => Array
                                    (
                                        [0] => altered
                                        [1] => hasShots
                                        [2] => housebroken
                                    )
                            )
                        [lastUpdate] => 2012-10-11T15:19:05Z
                        [media] => SimpleXMLElement Object
                            (
                                [photos] => SimpleXMLElement Object
                                    (
                                        [photo] => Array
                                            (
                                                [0] => http://photos.petfinder.com/photos/US/NC/NC416/11036032/NC416.11036032-1-x.jpg
                                                [1] => http://photos.petfinder.com/photos/US/NC/NC416/11036032/NC416.11036032-1-fpm.jpg
                                            )
                                    )
                            )
                        [contact] => SimpleXMLElement Object
                            (
                                [email] => kfkhgkhjg
                            )
                    )
                [2] => SimpleXMLElement Object ...

我需要能够按宠物名称或'lastUpdate'条目按字母顺序排序。这些将是单独的排序方法。