How to disable/enable keys

Can somebody correct what Im doing wrong here?

PHP Code:

$config = array(
array('field' => 'length', 'label' => 'Length', 'rules' => 'required|regex_match/[0-9.]/'', 'errors' => array( 'required' => 'Provide%s', '%sNumbersOnly')));
$this->form_validation->set_rules($config);