Move a specified value to the last position in an array without changing the position of keys

I need to shift an array with ID's so the ID(person) can't get his own ID unless the "game" is over.

So I got this:

$array = array(
    "2" => "2",
    "3" => "3",
    "6" => "6",
    "8" => "8",
    "12" => "12",
);

And I want it this way:

$array = array(
    "2" => "3",
    "3" => "6",
    "6" => "8",
    "8" => "12",
    "12" => "2",
);

So after long trying and getting some help from an old friend this is the final result:

    $prev = null;
    $firstIndex = null;
    foreach ($userArr as $i => $user) {
        if (is_null($prev)) {
            $firstIndex = $i;
            $prev = $user;
            continue;
        }
        $userArr[$i] = $prev;
        $prev = $user;
    }
    $userArr[$firstIndex] = $prev;