php求助將一，二級(jí)分類查詢結(jié)果拼成想要的json格式

不是特別明白 你想要的json格式， 按照我理解的意思 隨手寫了一段，并沒有測試

$res = $db->table('cate')->where('parentid =0')->select();
$array=array();
foreach ($res as $key =>$val){
    $cate = $db->table('cate')->where('parentid ='.$val['id'])->select();
    $array[$key]['id']=$cate['id'];
    $array[$key]['disabled']=false;
    $array[$key]['groupName']=$val['categoryname'];
    $array[$key]['groupId']=$val['id'];
    $array[$key]['selected']=false;
    $array[$key]['name']=$cate['categoryname'];
}
echo json_encode($array);exit;

$arr = [

['id'=>1,'parentid'=>0,'categoryname'=>'一級(jí)分類1'],
['id'=>2,'parentid'=>0,'categoryname'=>'一級(jí)分類2'],
['id'=>3,'parentid'=>0,'categoryname'=>'一級(jí)分類3'],
['id'=>4,'parentid'=>0,'categoryname'=>'一級(jí)分類4'],
['id'=>5,'parentid'=>1,'categoryname'=>'一級(jí)分類1-1'],
['id'=>6,'parentid'=>1,'categoryname'=>'一級(jí)分類1-2'],
['id'=>7,'parentid'=>2,'categoryname'=>'一級(jí)分類2-1'],
['id'=>8,'parentid'=>2,'categoryname'=>'一級(jí)分類2-2'],
['id'=>9,'parentid'=>3,'categoryname'=>'一級(jí)分類3-1'],
['id'=>10,'parentid'=>4,'categoryname'=>'一級(jí)分類4-1'],

];
$a = $b = $c = [];
foreach($arr as $k=>&$v){

if($v['parentid'] === 0) {

  $a[$k]['parentid'] = $v['categoryname'];

}elseif($v['parentid'] === 1){

  $b[$k]['parentid'] = $v['categoryname'];

}else{

     $c[$k]['parentid'] = $v['categoryname'];

}

}