将多维关联数组转置为根据外部关联键排序的多维索引数组

Question

I need to transpose a multidimensional associative array into a multidimensional indexed array sorted against and an external associative key. In the example below, I need a way to get from the 'input' to the 'expected output'.

I've tried array_match(), array_intersect() but I think I'm missing something. There must be an elegant solution to this but I cannot figure it out.

//Input  

  $array = array(
    array('Volvo' => 22, 'BMW' => 13, 'Saab' => 5, 'Land Rover' => 11),
    array('Nissan' => 10, 'Saab' => 4),
    array('Land Rover' => 22, 'BMW' => 9, 'Nissan' => 2, 'Ford' => 17)
    //...
  );

//Expected output  

  $array_cars = array(   // sorted list of unique car names
    0 => 'BMW',
    1 => 'Ford',
    2 => 'Land Rover',
    3 => 'Nissan',
    4 => 'Saab',
    5 => 'Volvo'
    //...
    );

  $compiled_data = array(    // 2D matrix, columns: $array, rows: $array_car
    array(0 => 13, 2 => 9),  // 'BMW'
    array(2 => 17),          // 'Ford'
    array(0 => 11, 2 => 22), // 'Land Rover'
    array(1 => 10, 2 => 2),  // 'Nissan'
    array(0 => 5, 1 => 4),   // 'Saab'
    array(1 => 22)           // 'Volvo'
    //...
);

Answer 1

Probably the simplest thing is to just iterate over all the values, sorting them into a car indexed array. You can then use ksort to sort the data:

$output = array();
foreach ($array as $key => $a) {
    foreach ($a as $car => $v) {
        $output[$car][$key] = $v;
    }
}
ksort($output);
$array_cars = array_keys($output);
$compiled_data = array_values($output);
var_export($array_cars);
var_export($compiled_data);

Output:

array (
  0 => 'BMW',
  1 => 'Ford',
  2 => 'Land Rover',
  3 => 'Nissan',
  4 => 'Saab',
  5 => 'Volvo',
)
array (
  0 => 
  array (
    0 => 13,
    2 => 9,
  ),
  1 => 
  array (
    2 => 17,
  ),
  2 => 
  array (
    0 => 11,
    2 => 22,
  ),
  3 => 
  array (
    1 => 10,
    2 => 2,
  ),
  4 => 
  array (
    0 => 5,
    1 => 4,
  ),
  5 => 
  array (
    0 => 22,
  ),
)

Demo on 3v4l.org