How to prevent duplication of php arrays, how to use key value, how to splice and split

foreach($a as $key=>$val){//key is the subscript of array $a $val is the value of $a
                  $val = array_unique($val);//This is to prevent duplication of array $val
                                $insertDate = array(//                                                                                                                        ’ having-to's having's
          ’ having having The value of the $a array explode is split
            );