How to randomize array from the range of indexes?

I am currently working on room assigning, how do I randomize array from only indexes 1 to 3? I have 4 indexes in my array.

$arrayroom = array("1","2","3","4");
$check1 = "SELECT COUNT(*) AS Total FROM grade_7 WHERE Room_Number = '1' ";
    $ch= mysqli_query($conn,$check1);
    $d = mysqli_fetch_assoc($ch);
    if($d['Total'] < 40){
        $room = $arrayroom[0];
     }
     else{
        $room = array_rand($arrayroom);
     }