Convert hierarchical multidimensional array into a 2d array

Question

I need to convert a hierarchical multidimensional array into a 2d array by recursively traversing each subset of data and push them into a result array.

Input:

$multi = [
    [
        'case_code_id' => 1,
        'parent_id' => 0,
        'case_code' => 'Main A',
        'sub_codes' => [
            [
                'case_code_id' => 3,
                'parent_id' => 1,
                'case_code' => 'Sub A',
                'sub_codes' => [
                    [
                        'case_code_id' => 5,
                        'parent_id' => 3,
                        'case_code' => 'Sub Sub A',
                        'sub_codes' => []
                    ]
                ]
            ],
            [
                'case_code_id' => 4,
                'parent_id' => 1,
                'case_code' => 'Sub B',
                'sub_codes' => []
            ]
        ]
    ],
    [
        'case_code_id' => 2,
        'parent_id' => 0,
        'case_code' => 'Main B',
        'sub_codes' => []
    ]
]

Desired result:

Array
(
    [0] => Array
    (
        [case_code_id] => 1
        [parent_id] => 0
        [case_code] => Main A
    )
    [1] => Array 
    (
        [case_code_id] => 3
        [parent_id] => 1
        [case_code] => Sub A
    )
    [2] => Array
    (
        [case_code_id] => 5
        [parent_id] => 3
        [case_code] => Sub Sub A
    )
    [3] => Array
    (
        [case_code_id] => 4
        [parent_id] => 1
        [case_code] => Sub B
    )
    [4] => Array
    (
        [case_code_id] => 2
        [parent_id] => 0
        [case_code] => Main B
    )
)

I have tried several loops but nothing returns the full array.

Here is what I have for my loop:

public function array_flatten($array, $list = array()) {
    for ($i = 0; $i < count($array); $i++) {
        $results[] = array(
            'case_code_id' => $array[$i]['case_code_id'],
            'case_code' => $array[$i]['case_code'],
            'parent_id' => $array[$i]['parent_id']
        );
        if (count($array[$i]['sub_codes']) > 0) {
            $this->array_flatten($array[$i]['sub_codes'], $results);
        } else {
            $results[] = $array[$i];
        }
    }
    return $results;
}

And I'm calling it like this: ($multi contains the multidimensional array)

$flat = $this->array_flatten($multi);

The variable $multi is created from this function:

public function build_case_code_tree(array $elements, $parentId = 0) {
    $branch = array();
    foreach ($elements as $element) {
        if ($element['parent_id'] == $parentId) {
            $children = $this->build_case_code_tree($elements, $element['case_code_id']);
            $element['sub_codes'] = $children;
            $branch[] = $element;
        }
    }
    return $branch;
}

Any thoughts?

Possible duplicate of How to "flatten" a multi-dimensional array to simple one in PHP? — Eliya Cohen
– Eliya Cohen, Commented Sep 25, 2018 at 19:45
The suggested post did not produce the results I'm looking for. This is what the output looked like Array ( [0] => 1 [1] => 0 [2] => Main A [3] => 3 [4] => 1 [5] => Sub A [6] => 5 [7] => 3 [8] => Sub Sub A [9] => 4 [10] => 1 [11] => Sub B [12] => 2 [13] => 0 [14] => Main B ) — Dan Glauber
– Dan Glauber, Commented Sep 25, 2018 at 19:47
It would be super helpful if you could provide the initiation of $multi for us instead of expecting us to mock up our own data based on your print_r(). It generally helps you to get relevant and working answers when you provide an easy way for us to test the sample data... — MonkeyZeus
– MonkeyZeus, Commented Sep 25, 2018 at 20:11

steffen · Accepted Answer · 2018-09-25 21:24:12Z

1

function array_flatten($a, $flat = []) {
    $entry = [];
    foreach ($a as $key => $el) {
        if (is_array($el)) {
            $flat = array_flatten($el, $flat);
        } else {
            $entry[$key] = $el;
        }
    }
    if (!empty($entry)) {
        $flat[] = $entry;
    }
    return $flat;
}
print_r(array_flatten($multi));

answered Sep 25, 2018 at 21:24

steffen

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Comments

henry700 · Accepted Answer · 2018-09-25 19:49:36Z

0

You're not using $list anywhere in the code, and nothing is passed by reference. You're close, but your function should use $list in the place of $results, and it should receive $list by reference and modifying it in place instead of returning it.

Something like this (untested though):

function array_flatten($array,&$list=array()){
    for ($i=0;$i<count($array);$i++) {
        $list[] = array(
            'case_code_id'=>$array[$i]['case_code_id'],
            'case_code'=>$array[$i]['case_code'],
            'parent_id'=>$array[$i]['parent_id']
        );
        if (count($array[$i]['sub_codes']) > 0) {
            $this->array_flatten($array[$i]['sub_codes'],$list);
        } else {
            $list[] = $array[$i];
        }
    }
}

And calling it like this:

$flat = Array();
$this->array_flatten($multi, $flat);
// Result is inside $flat now

answered Sep 25, 2018 at 19:49

henry700

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1 Comment

Dan Glauber Over a year ago

I updated the code, but not getting any results. Should there be a return?

mickmackusa · Accepted Answer · 2024-02-10 07:51:05Z

As you recursively traverse all levels and iterate each subset, temporarily hold the sub_code value, then remove the sub_code element from the subset. Push the trimmed subset into the result array and also feed the cached sub_code data into a recursive function call.

If the child was empty, then an empty array will be returned. If an empty array is "spread" as a parameter of array_push(), then nothing will be added to the array. Because the custom function call only returns a linear array of subsets, using the spread operator inside of array_push() means that recursive calls will never create unwanted depth.

Code: (Demo)

function flatten(array $array): array
{
    $result = [];
    foreach ($array as $v) {
        $subCode = $v['sub_codes'];
        unset($v['sub_codes']);
        array_push(
            $result,
            $v,
            ...flatten($subCode)
        );
        
    }
    return $result;
}

var_export(flatten($array));

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