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<?php $array = array( 55 => array( 'ident' => 'test 1', 'depth' => 1, ), 77 => array( 'parent_id' => 55, 'ident' => 'test 2', 'depth' => 2, ), 109 => array( 'parent_id' => 77, 'ident' => 'test 3', 'depth' => 3, ), 78 => array( 'parent_id' => 55, 'ident' => 'test 4', 'depth' => 2, ), 25 => array( 'ident' => 'test 5', 'depth' => 1, ) ); function v1($array) { foreach ($array as $key => &$sub) { if (isset($sub['parent_id'])) { $array[$sub['parent_id']]['children'][$key] = &$sub; } } unset($sub); // unset the reference to make sure to not overwrite it later... // now remove the entries with parents foreach ($array as $key => $sub) { if (isset($sub['parent_id'])) unset($array[$key]); } return $array; } function &find_by_key($key, $array) { var_dump($array); foreach($array as $k => &$v) { if($key == $k) { return $v; } } foreach($array as $sub) { if(isset($sub['children']) && FALSE !== ($found = &find_by_key($key, $sub['children']))) { return $found; } } return FALSE; } function v2($array) { $out = array(); foreach ($array as $key => $sub) { if(!isset($sub['parent_id'])) { $out[$key] = $sub; $out[$key]['children'] = array(); } else { $parent = &find_by_key($sub['parent_id'], $out); $parent['children'] = array(); $parent['children'][$key] = $sub; return $out; } } return $out; } //var_dump(v1($array)); var_dump(v2($array));

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