Convert a series of parent-child relationships into a tree?

Question

I am terribly stuck. I think I need to write a recursive method but I can't work out how...!

I am trying to convert an array of parent-child relationships into a hierarchical tree which I will later display to a user.

This is an example of the input data I might have:

$input = array(
    array(
            'itemGroupID' => 1,
            'childItemGroupID' => 2
        ),
    array(
            'itemGroupID' => 1,
            'childItemGroupID' => 3
        ),
    array(
            'itemGroupID' => 1,
            'childItemGroupID' => 4
        ),
    array(
            'itemGroupID' => 1,
            'childItemGroupID' => 212
        ),
    array(
            'itemGroupID' => 1,
            'childItemGroupID' => 339
        ),
    array(
            'itemGroupID' => 1,
            'childItemGroupID' => 336
        ),
    array(
            'itemGroupID' => 1,
            'childItemGroupID' => 6
        ),
    array(
            'itemGroupID' => 1,
            'childItemGroupID' => 5
        ),
    array(
            'itemGroupID' => 6,
            'childItemGroupID' => 8
        ),
    array(
            'itemGroupID' => 6,
            'childItemGroupID' => 9
        ),
    array(
            'itemGroupID' => 6,
            'childItemGroupID' => 10
        ),
    array(
            'itemGroupID' => 6,
            'childItemGroupID' => 11
        ),
    array(
            'itemGroupID' => 6,
            'childItemGroupID' => 12
        ),
    array(
            'itemGroupID' => 6,
            'childItemGroupID' => 13
        ),
    array(
            'itemGroupID' => 6,
            'childItemGroupID' => 74
        ),
    array(
            'itemGroupID' => 9,
            'childItemGroupID' => 15
        ),
    array(
            'itemGroupID' => 10,
            'childItemGroupID' => 16
        ),
    array(
            'itemGroupID' => 11,
            'childItemGroupID' => 17
        ),
    array(
            'itemGroupID' => 12,
            'childItemGroupID' => 18
        ),
    array(
            'itemGroupID' => 13,
            'childItemGroupID' => 19
        ),
    array(
            'itemGroupID' => 74,
            'childItemGroupID' => 75
        )
 );

I wish to get back data in a format like:

$output = array(
    array(
        'itemGroupID' => 1,
        'children' => array(
              array(
                  'itemGroupID' => 2                   
              ),
              array(
                  'itemGroupID' => 3                   
              ),
              array(
                  'itemGroupID' => 4                   
              ),
              array(
                  'itemGroupID' => 212                   
              ),
              array(
                  'itemGroupID' => 339                   
              ),
              array(
                  'itemGroupID' => 336                  
              ),
              array(
                  'itemGroupID' => 6,
                  'children' => array(
                      array(
                          'itemGroupID' => 8                  
                      ),
                      array(
                          'itemGroupID' => 9,
                          'children' => array(
                              array(
                                  'itemGroupID' => 15
                              )   
                          )                 
                      ), 
                      array(
                          'itemGroupID' => 10,
                          'children' => array(
                              array(
                                  'itemGroupID' => 16
                              )   
                          )                  
                      ), 
                      array(
                          'itemGroupID' => 11,
                          'children' => array(
                              array(
                                  'itemGroupID' => 17
                              )   
                          )                   
                      ), 
                      array(
                          'itemGroupID' => 12,
                          'children' => array(
                              array(
                                  'itemGroupID' => 18
                              )   
                          )                   
                      ), 
                      array(
                          'itemGroupID' => 13,
                          'children' => array(
                              array(
                                  'itemGroupID' => 19
                              )   
                          )                   
                      ), 
                      array(
                          'itemGroupID' => 74,
                          'children' => array(
                              array(
                                  'itemGroupID' => 75
                              )   
                          )                   
                      )                    
                  )               
              ),
              array(
                  'itemGroupID' => 5                   
              )
         )
    )
);

I managed to write some code which would tell me the root(s) to start from. (As I was worried that if you were recursing from the first node it might turn out that this is from half-way down the chain already...)

Btw, the element I output can be used to get the starting index, for each hierarchical chain.

private function _arraySearch($arr, $callback)
{
    foreach ($arr as $key => $item) {
        if ($callback($item)) {
            return $key;
        }
    }
    return false;
}

private function _findRootsOfItemGroupTree($activeItemGroupChildren)
{
    $searchArray = $activeItemGroupChildren;
    $roots = array();
    foreach ($activeItemGroupChildren as $itemGroupChild) {
        $parentItemGroupID = $itemGroupChild['itemGroupID'];

        $found = array_filter($searchArray, function ($element) use ($parentItemGroupID) {
            return $element['childItemGroupID'] == $parentItemGroupID;
        });

        $rootItemGroupID = $parentItemGroupID;
        if (count($found) == 0
            && $this->_arraySearch($roots,
                function ($element) use ($rootItemGroupID) {
                    return $element['itemGroupID'] == $rootItemGroupID;
                }) === false) {

            $roots[] = $itemGroupChild;
        }
    }
    return $roots;
}

However, I now need to use this information to create a new associative array. I can't work out how. (I will post some workings in a couple of minutes..)

Ideas?

note: assume there are no recursive loops in this structure even though they could technically exist.

Answer 1

If I understand your problem correctly, this should work. Notice how I call the orderMe function inside the function to make it recursive.

function orderMe($input, $parentId)
{
    $return = array($parentId => array('itemGroupID' => $parentId));
    $childs = array();
    foreach ($input as $i)
    {
        if ($i['itemGroupID'] == $parentId)
        {
            $return[$i['itemGroupID']]['children'][$i['childItemGroupID']] = array('itemGroupID' => $i['childItemGroupID']);
            $childs[] = $i['childItemGroupID'];
        }

        if (in_array($i['childItemGroupID'], $childs))
        {
            $allChilds = orderMe($input, $i['childItemGroupID']);
            if (!empty($allChilds[$i['childItemGroupID']]['children']))
                $return[$i['itemGroupID']]['children'][$i['childItemGroupID']] =  $allChilds;
        }
    }

    return $return;
}

print_r(orderMe($input, 1));

Outputs:

array (
  1 => 
  array (
    'itemGroupID' => 1,
    'children' => 
    array (
      2 => 
      array (
        'itemGroupID' => 2,
      ),
      3 => 
      array (
        'itemGroupID' => 3,
      ),
      4 => 
      array (
        'itemGroupID' => 4,
      ),
      212 => 
      array (
        'itemGroupID' => 212,
      ),
      339 => 
      array (
        'itemGroupID' => 339,
      ),
      336 => 
      array (
        'itemGroupID' => 336,
      ),
      6 => 
      array (
        6 => 
        array (
          'itemGroupID' => 6,
          'children' => 
          array (
            8 => 
            array (
              'itemGroupID' => 8,
            ),
            9 => 
            array (
              9 => 
              array (
                'itemGroupID' => 9,
                'children' => 
                array (
                  15 => 
                  array (
                    'itemGroupID' => 15,
                  ),
                ),
              ),
            ),
            10 => 
            array (
              10 => 
              array (
                'itemGroupID' => 10,
                'children' => 
                array (
                  16 => 
                  array (
                    'itemGroupID' => 16,
                  ),
                ),
              ),
            ),
            11 => 
            array (
              11 => 
              array (
                'itemGroupID' => 11,
                'children' => 
                array (
                  17 => 
                  array (
                    'itemGroupID' => 17,
                  ),
                ),
              ),
            ),
            12 => 
            array (
              12 => 
              array (
                'itemGroupID' => 12,
                'children' => 
                array (
                  18 => 
                  array (
                    'itemGroupID' => 18,
                  ),
                ),
              ),
            ),
            13 => 
            array (
              13 => 
              array (
                'itemGroupID' => 13,
                'children' => 
                array (
                  19 => 
                  array (
                    'itemGroupID' => 19,
                  ),
                ),
              ),
            ),
            74 => 
            array (
              74 => 
              array (
                'itemGroupID' => 74,
                'children' => 
                array (
                  75 => 
                  array (
                    'itemGroupID' => 75,
                  ),
                ),
              ),
            ),
          ),
        ),
      ),
      5 => 
      array (
        'itemGroupID' => 5,
      ),
    ),
  ),
)