Как значения php массива сделать ключами

$words = ['zero', 'one', 'two' ,'three'];
$numbers = [0, 1, 2, 3];
print_r(array_combine($words, $numbers));
# => [
# =>   "zero" => 0,
# =>   "one" => 1,
# =>   "two" => 2,
# =>   "three" => 3,
# => ]

print_r(array_flip($words));
# => [
# =>   "zero" => 0,
# =>   "one" => 1,
# =>   "two" => 2,
# =>   "three" => 3,
# => ]