How to Efficiently Build a Tree Structure from a Hierarchical Array List?

Building a Tree Structure from an Array List

Given an array list of items with hierarchical relationships, how can we efficiently transform it into a nested tree structure?

Solution:

To achieve this conversion without using complex database optimizations, we can employ a recursive function:

$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;
}

This code arranges the items into a nested hierarchical structure, representing the parent-child relationships among them. The resulting tree structure can be printed using print_r.

By leveraging a recursive function, we can efficiently transform an array list into a tree structure, allowing for easy navigation and organization of data.

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