array-sort-parent-child.php

<?php
/*source: https://stackoverflow.com/questions/26848825/php-sorting-array-by-id-and-parent-id*/

$arr = array(
  array('id' => 1, 'parent' => 0, 'title' => 'XXX1', 'children'=>array()),
  array('id' => 85, 'parent' => 0, 'title' => 'XXX2', 'children'=>array()),
  array('id' => 41, 'parent' => 0, 'title' => 'XXX2', 'children'=>array()),
  array('id' => 17, 'parent' => 0, 'title' => 'XXX3', 'children'=>array()),
  array('id' => 66, 'parent' => 1, 'title' => 'XXX4', 'children'=>array()),
  array('id' => 92, 'parent' => 1, 'title' => 'XXX5', 'children'=>array()),
  array('id' => 65, 'parent' => 1, 'title' => 'XXX6', 'children'=>array()),
  array('id' => 45, 'parent' => 41, 'title' => 'XXX7', 'children'=>array()),
  array('id' => 19, 'parent' => 92, 'title' => 'XXX8', 'children'=>array()),
  array('id' => 101, 'parent' => 45, 'title' => 'XXX9', 'children'=>array()),
  array('id' => 102, 'parent' => 45, 'title' => 'XXX10', 'children'=>array()),
  array('id' => 103, 'parent' => 19, 'title' => 'XXX11', 'children'=>array()),
  array('id' => 104, 'parent' => 19, 'title' => 'XXX12', 'children'=>array()),
  array('id' => 105, 'parent' => 19, 'title' => 'XXX13', 'children'=>array())
);

$newArr = unflattenArray($arr);

echo "<pre>";
print_r($newArr);
echo "</pre>";


function unflattenArray($flatArray){
  $refs = array(); //for setting children without having to search the parents in the result tree.
    $result = array();

    //process all elements until nohting could be resolved.
    //then add remaining elements to the root one by one. 
    while(count($flatArray) > 0){
        for ($i=count($flatArray)-1; $i>=0; $i--){
            if ($flatArray[$i]["parent"]==0){
                //root element: set in result and ref!
                $result[$flatArray[$i]["id"]] = $flatArray[$i]; 
                $refs[$flatArray[$i]["id"]] = &$result[$flatArray[$i]["id"]];
                unset($flatArray[$i]);
        $flatArray = array_values($flatArray);
            }

            else if ($flatArray[$i]["parent"] != 0){
                //no root element. Push to the referenced parent, and add to references as well. 
                if (array_key_exists($flatArray[$i]["parent"], $refs)){
                    //parent found
                    $o = $flatArray[$i];
                    $refs[$flatArray[$i]["id"]] = $o;
          $refs[$flatArray[$i]["parent"]]["children"][] = &$refs[$flatArray[$i]["id"]];
                    unset($flatArray[$i]);
          $flatArray = array_values($flatArray);
                }
            }
        }
  }
  return $result;
}


/*sorting*/
sortMyArrays($newArr);
echo "<pre>";
print_r($newArr);
echo "</pre>";

function sortMyArrays(&$arr){
   uasort($arr, "srt");
   foreach ($arr as $a) {
     sortMyArrays($a["children"]);
   }
}

function srt($a, $b){
  return $a["id"] - $b["id"];
}
?>