php aggregate

test.php

$new_array = array();
foreach($array as $vehicle_id) {
  if(isset($new_array[$vechicle_id])) {
    $new_array[$vehicle_id] += 1;
  } else {
    $new_array[$vehicle_id] = 1;
  }
}

function sum($carry, $vehicle_id) {
  $carry[$vehicle_id] +1;
  return $carry
}

array_reduce($carry, $vechicle_array, array());