In php how to get all keys of multidimensional array with unknown depth

Question

I need to get all the keys from this array. I tried with a recursive call but only get first element keys. I want all the array keys to store into the array with level. means keys[0] = array(540,198). below is the array that I want to traverse and get all the keys. I had worked on more than 1 day but not get anything please help to fix this.

(
    [ch] => Array
        (
            [540] => Array
                (
                    [194] => Array
                        (
                            [16] => Array
                                (
                                    [144] => Array
                                        (
                                        )

                                    [145] => Array
                                        (
                                        )

                                    [146] => Array
                                        (
                                        )

                                    [147] => Array
                                        (
                                        )

                                    [148] => Array
                                        (
                                        )

                                    [195] => Array
                                        (
                                        )

                                    [199] => Array
                                        (
                                        )

                                    [149] => Array
                                        (
                                        )

                                    [200] => Array
                                        (
                                        )

                                    [150] => Array
                                        (
                                        )

                                    [444] => Array
                                        (
                                        )

                                    [151] => Array
                                        (
                                        )

                                    [445] => Array
                                        (
                                        )

                                    [446] => Array
                                        (
                                        )

                                    [152] => Array
                                        (
                                        )

                                )

                        )

                )

            [198] => Array
                (
                    [194] => Array
                        (
                            [16] => Array
                                (
                                    [144] => Array
                                        (
                                        )

                                    [145] => Array
                                        (
                                        )

                                    [146] => Array
                                        (
                                        )

                                    [147] => Array
                                        (
                                        )

                                    [148] => Array
                                        (
                                        )

                                    [195] => Array
                                        (
                                        )

                                    [199] => Array
                                        (
                                        )

                                    [149] => Array
                                        (
                                        )

                                    [200] => Array
                                        (
                                        )

                                    [150] => Array
                                        (
                                        )

                                    [444] => Array
                                        (
                                        )

                                    [151] => Array
                                        (
                                        )

                                    [445] => Array
                                        (
                                        )

                                    [446] => Array
                                        (
                                        )

                                    [152] => Array
                                        (
                                        )

                                )

                        )

                )

        )

)
$this->checkProductConfiguraions($configuraion,$count,$levelKeys);
function checkProductConfiguraions($configuraion,$count,$levelKeys) {
    foreach ($configuraions as $configuraion) {
        if (is_array($configuraion)) {
                $parentKeys = array_keys($configuraion);
                if(isset($levelKeys[$count])){
                    $levelKeys[$count] = array_unique(array_merge($levelKeys[$count],$parentKeys));
                } else {
                    $levelKeys[$count] = $parentKeys;
                }

                $count++;
                $levelKeys[$count] = array();
                for($i=0;$i<count($parentKeys);$i++){
                    $levelKeys[$count] = array_unique(array_merge($levelKeys[$count],array_keys($configuraion[$parentKeys[$i]])));
                    if(is_array($configuraion)){
                        $levelKeys = $this->checkProductConfiguraions($configuraion,$count,$levelKeys);
                    }
                }
        }
    }
}

Answer 1

function check($configurations, $count = 0, $levelKeys = array())
{
    foreach ($configurations as $k => $configuration) {
        if (!array_key_exists($count, $levelKeys) || 
            !in_array($k, $levelKeys[$count], true)) {
            $levelKeys[$count][] = $k;
        }
        if (!empty($configuration)) {
            $levelKeys = $this->check($configuration, $count + 1, $levelKeys);
        }
    }
    return $levelKeys;
}

DEMO

During the first round I fill the $levelKeys variable with the first key.

In the first IF I use in_array() and array_key_exist() to avoid duplicate values.

If the array I'm analyzing has a nested array I call the check() function passing: nested array, level I have reached, levelKeys.