Question

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Converting an array from one to multi-dimensional based on parent ID values

I am working in PHP.

I have the following array that has relational data (parent child relationships).

Array        
(        
    [5273] => Array        
        (        
            [id] => 5273        
            [name] => John Doe        
            [parent] =>         
        )        

    [6032] => Array        
        (        
            [id] => 6032        
            [name] => Sally Smith        
            [parent] => 5273        
        )        

    [6034] => Array        
        (        
            [id] => 6034        
            [name] => Mike Jones        
            [parent] => 6032        
        )        

    [6035] => Array        
        (        
            [id] => 6035        
            [name] => Jason Williams        
            [parent] => 6034        
        )        

    [6036] => Array        
        (        
            [id] => 6036        
            [name] => Sara Johnson        
            [parent] => 5273        
        )        

    [6037] => Array        
        (        
            [id] => 6037        
            [name] => Dave Wilson        
            [parent] => 5273        
        )        

    [6038] => Array        
        (        
            [id] => 6038        
            [name] => Amy Martin        
            [parent] => 6037        
        )        
)        

I need it to be in this JSON format:

{        
   "id":"5273",        
   "name":"John Doe",        
   "data":{        

   },        
   "children":[        
      {        
         "id":" Sally Smith",        
         "name":"6032",        
         "data":{        

         },        
         "children":[        
            {        
               "id":"6034",        
               "name":"Mike Jones",        
               "data":{        

               },        
               "children":[        
                  {        
                     "id":"6035",        
                     "name":"Jason Williams",        
                     "data":{        

                     },        
                     "children":[        
                        {        
                           "id":"node46",        
                           "name":"4.6",        
                           "data":{        

                           },        
                           "children":[        

                           ]        
                        }        
                     ]        
                  }        
               ]        
            },        
            {        
               "id":"6036",        
               "name":"Sara Johnson",        
               "data":{        

               },        
               "children":[        

               ]        
            },        
            {        
               "id":"6037",        
               "name":"Dave Wilson",        
               "data":{        

               },        
               "children":[        
                  {        
                     "id":"6038",        
                     "name":"Amy Martin",        
                     "data":{        

                     },        
                     "children":[        

                     ]        
                  }        
               ]        
            }        
         ]        
      }        
   ]        
}        

I know I need to create a multidimensional array and run it through json_encode(). I also believe this method used to do this needs to be recursive because the real world data could have an unknown number of levels.

I would be glad to show some of my approaches but they have not worked.

Can anyone help me?

I was asked to share my work. This is what I have tried but I have not gotten that close to I don’t know how helpful it is.

I made an array of just the relationships.

foreach($array as $k => $v){
    $relationships[$v['id']] = $v['parent'];
}

I think (based off another SO post) used this relational data to create a the new multidimensional array. If I got this to work I was going to work on adding in the correct “children” labels etc.

$childrenTable = array();
    $data = array();
    foreach ($relationships as $n => $p) {
      //parent was not seen before, put on root
      if (!array_key_exists($p, $childrenTable)) {
          $childrenTable[$p] = array();
          $data[$p] = &$childrenTable[$p];  
      }
      //child was not seen before
      if (!array_key_exists($n, $childrenTable)) {
          $childrenTable[$n] = array();
      }
      //root node has a parent after all, relocate
      if (array_key_exists($n, $data)) {
          unset($data[$n]);
      }
      $childrenTable[$p][$n] = &$childrenTable[$n];      
    }
    unset($childrenTable);

print_r($data);

Answer 1

<?php
header('Content-Type: application/json; charset="utf-8"');

/**
 * Helper function
 * 
 * @param array   $d   flat data, implementing a id/parent id (adjacency list) structure
 * @param mixed   $r   root id, node to return
 * @param string  $pk  parent id index
 * @param string  $k   id index
 * @param string  $c   children index
 * @return array
 */
function makeRecursive($d, $r = 0, $pk = 'parent', $k = 'id', $c = 'children') {
  $m = array();
  foreach ($d as $e) {
    isset($m[$e[$pk]]) ?: $m[$e[$pk]] = array();
    isset($m[$e[$k]]) ?: $m[$e[$k]] = array();
    $m[$e[$pk]][] = array_merge($e, array($c => &$m[$e[$k]]));
  }

  return $m[$r][0]; // remove [0] if there could be more than one root nodes
}

echo json_encode(makeRecursive(array(
  array('id' => 5273, 'parent' => 0,    'name' => 'John Doe'),  
  array('id' => 6032, 'parent' => 5273, 'name' => 'Sally Smith'),
  array('id' => 6034, 'parent' => 6032, 'name' => 'Mike Jones'),
  array('id' => 6035, 'parent' => 6034, 'name' => 'Jason Williams'),
  array('id' => 6036, 'parent' => 5273, 'name' => 'Sara Johnson'),
  array('id' => 6037, 'parent' => 5273, 'name' => 'Dave Wilson'),
  array('id' => 6038, 'parent' => 6037, 'name' => 'Amy Martin'),
)));

demo: https://3v4l.org/s2PNC