<?php

/*
    Sample data.
*/
$items = array(
   array('id'=>1, 'title'=>'Home',     'parent_id'=>0),
   array('id'=>2, 'title'=>'News',     'parent_id'=>1),
   array('id'=>3, 'title'=>'Sub News', 'parent_id'=>2),
   array('id'=>4, 'title'=>'Articles', 'parent_id'=>0),
   array('id'=>5, 'title'=>'Article',  'parent_id'=>4),
   array('id'=>6, 'title'=>'Article2', 'parent_id'=>4)
);

/*
    Group by parent.
*/
$itemsByParent = array();
foreach ($items as $item)
{
  if (!isset($itemsByParent[$item['parent_id']]))
      $itemsByParent[$item['parent_id']] = array();

  $itemsByParent[$item['parent_id']][] = $item;
}

/*
    Print list recursively.
*/
function printList($items, $parentId = 0)
{
   echo '<ul>';
   foreach ($items[$parentId] as $item)
   {
       echo '<li>';
       echo $item['title'];
       $curId = $item['id'];
       //if there are children
       if (!empty($items[$curId]))
       {
           printList($items, $curId);
       }           
       echo '</li>';
   }
   echo '</ul>';
}

/*
    Finds top parent given node id
*/
function findTopParent($id,$ibp)
{
    foreach($ibp as $parentID=>$children)
    {
        foreach($children as $child)
        {
          if($child['id']==$id)
          {
            if($child['parent_id']!=0)
               return findTopParent($child['parent_id'],$ibp);
             else
               return $child;
          }
        }
    }
}

/*
    Get all parents, aka. breadcrumbs.
*/
function getAllParents($id,$ibp)
{
  foreach($ibp as $parentID=>$nodes)
  {
    foreach($nodes as $node)
    {
       if($node['id']==$id)
       {
          if($node['parent_id']!=0)
          {
             $a=getAllParents($node['parent_id'],$ibp);
             array_push($a,$node['parent_id']);
             return $a;
          }
          else
            return array();
       }
    }
  }
}

/*
    Gets all subnodes; children, grand children, etc...
*/
 function getDescendants($id,$ibp)
 {
     if(array_key_exists($id,$ibp))
     {
         $kids=array();
         foreach($ibp[$id] as $child)
         {
            array_push($kids,$child['id']);
            
            if(array_key_exists($child['id'],$ibp))
                $kids=array_merge($kids,getDescendants($child['id'],$ibp));
         }
         return $kids;
     }
     else
        return array();//supplied $id has no kids
}

// Print it!!
printList($itemsByParent);

// Find top parent!!
print_r(findTopParent(6,$itemsByParent));
/*
Array
(
    [id] => 4
    [title] => Articles
    [parent_id] => 0
)
*/

// Find path!!
print_r(getAllParents(3,$itemsByParent));
/*
Array
(
    [0] => 1
    [1] => 2
)
*/

print_r(getDescendants(1,$itemsByParent));
/*
Array
(
    [0] => 2
    [1] => 3
)
*/

print_r(getDescendants(4,$itemsByParent));
/*
Array
(
    [0] => 5
    [1] => 6
)
*/

print_r(getDescendants(0,$itemsByParent));
/*
Array
(
    [0] => 1
    [1] => 2
    [2] => 3
    [3] => 4
    [4] => 5
    [5] => 6
)
*/

Output of printList:

• Home
  • News
    • Sub News
• Articles
  • Article
  • Article2

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