วิธีการหาตัวเลขแบบไม่ซ้ำ ใน array

<?php
$num=3;
$arr = array("1","2","3","4","5","6","7","8");
$count_arr=count($arr);
 
$arrName= array();
 
$idx=0;
 
while($idx<$num) 
{
	$id_rand = rand(0,$count_arr-1);
	if (!in_array($arr[$id_rand],$arrName))
	{
		$arrName[$idx]=$arr[$id_rand];
		$idx++;
	}
} 
 
print_r($arrName);
?>