I want to stress that in the user function, you do need to return either a 1 or a -1 properly; you cannot simply return 0 if the results are equal and 1 if they are not. The following code is incorrect:<?phpfunction myfunction($v1,$v2) {if ($v1===$v2) { return 0; }return 1;}$a1=array(1, 2, 4);$a2=array(1, 3, 4);print_r(array_uintersect($a1,$a2,"myfunction"));?>This code is correct:<?phpfunction myfunction($v1,$v2) {if ($v1===$v2) { return 0; }if ($v1 > $v2) return 1;return -1;}$a1=array(1, 2, 4);$a2=array(1, 3, 4);print_r(array_uintersect($a1,$a2,"myfunction"));?>