PHP function to remove duplicate elements from an array and sort by key_PHP tutorial

1. The role of this function: remove duplicate elements in the array and sort by key name
function assoc_unique($arr, $key) {
$tmp_arr = array();
foreach($arr as $k => $v) {
if(in_array($v[$key], $tmp_arr)) {
unset($arr[$k]);
} else {
$tmp_arr [] = $v[$key];
}
}
sort($arr);
return $arr;
}

Usage example:
$aa = array(
array('id' => 123, 'name' => 'Zhang San'),
array('id' => 123, 'name' => ' Li Si'),
array('id' => 124, 'name' => 'Wang Wu'),
array('id' => 125, 'name' => ' Zhao Liu'),
array('id' => 126, 'name' => 'Zhao Liu')
);
$key = 'id';
assoc_unique(& $aa, $key);
print_r($aa);