PHP数组去重..............过滤字段

$test_data = M('hot');  //实例化数据表
$data = $test_data->Distinct(true)->field('descriprion')->order('description desc')->select();  //利用distinct方法去重
$data = $test_data->group('department')->order('description desc')->select();  //利用group方法去重
dump($data);