直接访问数组中的对象

Question

I have the results of a database query stored in a variable $lists

print_r gives me the following output:

DB Object
(
     [_pdo:DB:private] => PDO Object
          (
          )

     [_query:DB:private] => PDOStatement Object
          (
                [queryString] => SELECT * FROM lists
          )

     [_error:DB:private] => 
     [_results:DB:private] => Array
          (
                [0] => stdClass Object
                     (
                          [id] => 10
                          [list_name] => Farmer
                     )

                [1] => stdClass Object
                     (
                          [id] => 11
                          [list_name] => Gardener
                     )

                [2] => stdClass Object
                     (
                          [id] => 12
                          [list_name] => Plumber
                     )

          )

     [_count:DB:private] => 3
)

By using a for loop I can access the list_names as follows:

foreach ($lists->results() as $person) {
    echo $person->list_name;
}

This gives me: Farmer Gardener Plumber

What I want to do is directly access the list_name but I simply can't understand how to.