create array tree from array list

Question

i have a list like this:

array(
  array(id=>100, parentid=>0, name=>'a'),
  array(id=>101, parentid=>100, name=>'a'),
  array(id=>102, parentid=>101, name=>'a'),
  array(id=>103, parentid=>101, name=>'a'),
)

but way bigger so i need a efficient way to make this into a tree like structure like this:

array(
  id=>100, parentid=>0, name=>'a', children=>array(
    id=>101, parentid=>100, name=>'a', children=>array(
      id=>102, parentid=>101, name=>'a',
      id=>103, parentid=>101, name=>'a',
    )
  )
)

i cannot use things like nested set or things like that becoas i can add left and right values in my database. any ideas?

Answer 1

oke this is how i solved it:

$arr = array(
  array('id'=>100, 'parentid'=>0, 'name'=>'a'),
  array('id'=>101, 'parentid'=>100, 'name'=>'a'),
  array('id'=>102, 'parentid'=>101, 'name'=>'a'),
  array('id'=>103, 'parentid'=>101, 'name'=>'a'),
);

$new = array();
foreach ($arr as $a){
    $new[$a['parentid']][] = $a;
}
$tree = createTree($new, array($arr[0]));
print_r($tree);

function createTree(&$list, $parent){
    $tree = array();
    foreach ($parent as $k=>$l){
        if(isset($list[$l['id']])){
            $l['children'] = createTree($list, $list[$l['id']]);
        }
        $tree[] = $l;
    } 
    return $tree;
}