Recursively loop through multidimensional to create flat array

Question

I have a multidimensional array that looks like this:

$trees = array(
    array(
        'name' => 'Parent',
        '__children' => array(
            array(
                'name' => 'Child'
            ),
            array(
                'name' => 'Second Child'
            )
        )
    )
);

The depth of the array is unknown and I need to recursively flatten it. So it looks more like this:

array(
  array(
    'name' => 'Parent' 
  ),
  array(
    'name' => 'Child' 
  ),
  array(
    'name' => 'Second Child' 
  )
)

I thought something like this might work:

public function flattenTree($trees, $tree = array())
{
    foreach($trees as $item){
        //$i = 1, 2, then 3
        $i = count($tree);
        $tree[$i] = array('name' => $item['name']);
        if(isset($item['__children']))
            $this->flattenTree($item['__children'], $tree);
    }
    return $tree;
}

But this is only gives me :(

Array
(
    [0] => Array
        (
            [name] => Parent
        )

)

I am unsure how to do this. Is it possible?

As a bonus I really need the output array to look like this(notice the name value changed) :)

array(
  array(
    'name' => 'Parent' 
  ),
  array(
    'name' => 'Parent Child' 
  ),
  array(
    'name' => 'Parent Second Child' 
  )
)

Thanks a ton for the help on this one. Looking forward to the solutions. I am stumped!

possible duplicate of [How to Flatten a Multidimensional Array?](http://stackoverflow.com/questions/1319903/how-to-flatten-a-multidimensional-array) — John Conde, Nov 18 '12 at 18:24
You can't specify an array element without a index. I'm sure you have got the correct output now — Mohamed Navas, Nov 18 '12 at 18:30
@mohamed yes. For some reason the output does not contain the children — Mike, Nov 18 '12 at 19:54
@JohnConde any chance you can take the example from that link and apply it here? I am not sure exactly how it would work, especially with building the full name based on the tree. — Mike, Nov 18 '12 at 20:45
Do I gather correctly from your post that you actually want to string prepend the originial parent name 'Parent' to the child name? — Pankrates, Nov 18 '12 at 21:13
@pankrates that is correct. I would like to get the first part working. But then I need to prepend the name like I show in the last code block. — Mike, Nov 18 '12 at 21:14

score 1 · Answer 1 · answered Nov 18 '12 at 21:59

Ok I have given this a shot and although it might not be the cleanest solution I think it should get the job done:

function flattenRecursive(array &$flat, $parentkey, array $nested){

    $flag       = true;
    $prepend    = '';

    foreach( $nested as $k => $val ){
        if( is_array($val) ){

            if ( $k == '__children' && $flag) {
                $prepend = end($flat);
                $flag = true;
            } else {
                $flag = false;
            }

            flattenRecursive($flat, $prepend , $val);

        } else {

            $flat[] = $parentkey . ' ' . $val;

        }
    }
}

function flatten(array $nested){
    $flat = array();
    flattenRecursive($flat, '', $nested);
    return $flat;
}

On a test array (with extra nesting for extra testing) as follows

$trees = array(
            array(
                'name' => 'Parent',
                '__children' => array(
                    array(
                        'name' => 'Child',
                        '__children' => array(
                            array(
                                'name' => 'Nest One'
                            ),
                            array(
                                'name' => 'Nest Two'
                            )
                        )
                    ),
                    array(
                        'name' => 'Second Child'
                    )
                )
            )
        );

$result = flatten($trees);

the var_dump of $result looks like the following

array(5) {
  [0]=>
  string(7) " Parent"
  [1]=>
  string(13) " Parent Child"
  [2]=>
  string(22) " Parent Child Nest One"
  [3]=>
  string(22) " Parent Child Nest Two"
  [4]=>
  string(20) " Parent Second Child"
 }

Hopefully this was what you were looking for

Hi Pankrates, I think you are on to something here. However this does not work for me b/c the array is more complex than this and using the foreach( $nested as $k => $val ) is throwing things off. Can you translate this so it uses foreach( $nested as $item ) instead? — Mike, Nov 18 '12 at 23:09
Could you give an example array that is failing and where it is failing on? Find it hard to pinpoint what you mean exactly without example — Pankrates, Nov 19 '12 at 07:47
See my answer, thanks again for your efforts! It helped a lot. — Mike, Nov 19 '12 at 17:17

score 0 · Accepted Answer · answered Nov 19 '12 at 17:16

I ended up using something like this, with a lot of inspiration from @Pankrates answer. Thanks a lot.

$trees = $multidimensionalArray;
$flat = array();
$postRepository->flattenRecursive($flat, $trees);
//$flat is now a flattened version of $multidimensionalArray
var_dump($flat);


public function flattenRecursive(array &$flat, array $nested, $parentPrepend = false)
{
    foreach( $nested as $item ){
        $flat[] = array(
            'name' => ($parentPrepend) ? $parentPrepend . '/' . $item['name'] : $item['name']
        );
        $prepend = $parentPrepend ? $parentPrepend . '/' . $item['name'] : $item['name'];
        if(isset($item['__children']))
            $this->flattenRecursive($flat, $item['__children'], $prepend);
    }
}

score 0 · Answer 3 · answered Nov 22 '12 at 04:23

code

<?php


$output_array = array();

$input_array  = array(
    array(
        'name'=>'Parent',
        '__children' => array(
            array(
                'name' => 'Child'
            ),
            array(
                'name' => 'Second Child'
            )
        )
    )
);

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


function flatten($arr){
    global $output_array;
    if(is_array($arr)){
        foreach($arr as $key=>$value){
            if($key=="name" && !is_array($value)){
                $output_array[] = array($key=>$value);
            }
            elseif(is_array($value)){
                flatten($value);
            }
        }
    }
}

flatten($input_array);

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

Output

//Input array
Array
(
    [0] => Array
        (
            [name] => Parent
            [__children] => Array
                (
                    [0] => Array
                        (
                            [name] => Child
                        )

                    [1] => Array
                        (
                            [name] => Second Child
                        )

                )

        )

)

//Output Array
Array
(
    [0] => Array
        (
            [name] => Parent
        )

    [1] => Array
        (
            [name] => Child
        )

    [2] => Array
        (
            [name] => Second Child
        )

)

score 0 · Answer 4 · answered Jul 05 '21 at 07:40

I have similar logic problem, I used @Mike answer with some refactoring.

public function flattenRecursive(array &$flat, array $nested, $parentPrepend = false)
{
    foreach( $nested as $item ){
        $prepend = $parentPrepend ? $parentPrepend . '/' . $item['name'] : $item['name'];
        $flat[] = array(
            'name' => $prepend
        );
        if(isset($item['__children']))
            $this->flattenRecursive($flat, $item['__children'], $prepend);
    }
}

Recursively loop through multidimensional to create flat array

4 Answers4

Linked