PHP foreach injecting new index out of order on some iterations

Question

I have this method that will take a single dimension array and transform it into a multi-dimensional array. It's an adjacency list of categories. I'm injecting an enumerated path as I go. It works 90% of the time.

public function fnExpandArray($aData){

    $aNested = array();

    foreach($aData as &$aCat){

        if(isset($aData[$aCat['parent_id']])){

            $aData[$aCat['parent_id']]['sub'][$aCat['id']] = &$aCat;
            $aData[$aCat['parent_id']]['sub'][$aCat['id']]['path'] = $aData[$aCat['parent_id']]['path'] . '_' . $aCat['id'];

        } else {

            $aNested[$aCat['id']] = &$aCat;
            $aNested[$aCat['id']]['path'] = $aCat['id'];

        }

    }

    unset($aCat);
    return $aNested;
}

This works OK 90% of the time, however the "path" index that is being injected is sometimes being injected after the "sub" index and causing the enumerated path to be calculated incorrectly. Example:

Correct:

 [18] => Array
                    (
                        [id] => 18
                        [parent_id] => 1
                        [title] => Category 1
                        [path] => 1_18
                        [sub] => Array
                            (
                                [150] => Array
                                    (
                                        [id] => 150
                                        [parent_id] => 18
                                        [title] => Category 2
                                        [path] => 1_18_150

But in some iterations it'll inject 'path' after 'sub' and the routine will fail.

Fail:

  [45] => Array
                    (
                        [id] => 45
                        [parent_id] => 2
                        [sub] => Array
                            (
                                [10] => Array
                                    (
                                        [id] => 10
                                        [parent_id] => 45
                                        [sub] => Array
                                            (
                                                [152] => Array
                                                    (
                                                        [id] => 152
                                                        [parent_id] => 10
                                                        [title] => Category 1
                                                        [path] => _152
                                                    )

                                                [79] => Array
                                                    (
                                                        [id] => 79
                                                        [parent_id] => 10
                                                        [title] => Category 2
                                                        [path] => _10_79
                                                    )


                                            )

                                        [title] => Dryers
                                        [path] => _10

Note how path and title are injected after the sub injection. Any idea why?

I suspect it's because you're using references. Are you sure you need this? — Barmar, May 16 '16 at 21:55

score 0 · Answer 1 · edited May 23 '17 at 11:52

This method rewrite resolved my issue. Made multiple passes on the array.

public function fnExpandTaxonomy(&$aData) {

    $aTree = array();

    // Loop original flat array, build associative and inject additional indices as required. 
    foreach($aData as $iKey => &$aCat){
        $aTree[$aCat['id']] = &$aCat;
        $aTree[$aCat['id']]['level'] = 0; 
        $aTree[$aCat['id']]['path'] = $aCat['id']; 
        $aTree[$aCat['id']]['sub'] = array(); 
    }

    // Loop - Add children to parents. 
    foreach($aTree as $iKey => &$aCat) {
        if(!$aCat['parent_id']) continue;

        unset($aCat['level'],$aCat['path'],$aCat['sub']);
        $aCat['level'] = $aTree[$aCat['parent_id']]['level']+1; 
        $aCat['path'] = $aTree[$aCat['parent_id']]['path'].'_'.$aCat['id']; 
        $aTree[$aCat['parent_id']]['sub'][$aCat['id']] = &$aCat;

    }

    // Loop again, remove any items that don't have a parent of 0;
    foreach($aTree as $iKey => &$aCat) {
      if(!$aCat['parent_id']) continue;
      unset($aTree[$iKey]);
    }

    unset($aCat);
    return $aTree;  

}

Big thank you to pyson, whose answer (below) in another similar thread helped me out.

create array tree from array list

PHP foreach injecting new index out of order on some iterations

1 Answers1