PHP array_diff_ukey() Function

<?php
function myfunction($v1,$v2)
{
if ($v1===$v2)
{
return 0;
}
if ($v1>$v2)
{
return 1;
}
else
{
return -1;
}
}
$a1=array(0=>"Dog",1=>"Cat",2=>"Horse");
$a2=array(3=>"Rat",1=>"Bird",5=>"Monkey");
print_r(array_diff_ukey($a1,$a2,"myfunction"));
?>