Get all values and associative keys as a flat array from a multidimensional array of variable depth/structure

Question

Is there any way to flatten a multidimensional (1 to 3 levels max) with keys?

I have an array like this

array(
    'Orange',
    'Grape',
    'Banana' => array(
        'Big',
        'Small'
    ),
    'Apple' => array(
        'Red',
        'Green' => array(
            'Soft',
            'Hard'
        )
    )
);

And I want it to be like this

array(
    'Orange',
    'Grape',
    'Banana',
    'Big',
    'Small',
    'Apple',
    'Red',
    'Green',
    'Soft',
    'Hard'
);

So it will keep the order of appearance in order to lately get indexes with array_keys.

I've tried several ways but if the array elements a key for a new array, it wont be flattened, just skipped, so my final array looks like this

array:7 [▼
  0 => "Orange"
  1 => "Grape"
  2 => "Big"
  3 => "Small"
  4 => "Red"
  5 => "Soft"
  6 => "Hard"
]

Answer 1

You can write a recursive function for that:

$nested = array(
    'Orange',
    'Grape',
    'Banana' => array(
        'Big',
        'Small'
    ),
    'Apple' => array(
        'Red',
        'Green' => array(
            'Soft',
            'Hard'
        )
    )
);

function flattern($array)
{
    $flat=[];
    foreach($array as $key=>$val){
        if(is_array($val)){
            $flat[]=$key;
            $flat = array_merge($flat, flattern($val));
        }else{
            $flat[]=$val;
        }
    }
    return $flat;
}

var_dump(flattern($nested));