อยาก Sort value ใน Array 2 ครั้งอ่ะครับ PHP ครับ มีตัวอย่างด้านใน

<?php
$data[0]['GUEST'] = 1;
$data[0]['BAMOUNT'] = 500;
$data[1]['GUEST'] = 2;
$data[1]['BAMOUNT'] = 500;
$data[2]['GUEST'] = 1;
$data[2]['BAMOUNT'] = 100;
$data[3]['GUEST'] = 2;
$data[3]['BAMOUNT'] = 100;
$data[4]['GUEST'] = 3;
$data[4]['BAMOUNT'] = 1500;
$data[5]['GUEST'] = 1;
$data[5]['BAMOUNT'] = 1000;

usort($data, 'compare');

function compare($x, $y)
{
	if($x===$y) return 0;
	if ($x['GUEST'] < $y['GUEST']) { return -1;}
	else if ($x['GUEST'] == $y['GUEST']) { 
		if ($x['BAMOUNT'] < $y['BAMOUNT']) { return -1;}
	}
	return 1;

}
echo '<pre>'.print_r($data, true).'</pre>';