how to update or add a value to an existing json array using PHP forms?

I have a json array stored as a field in a database table. Now I want to use add, edit and delete functions on them. The following code modifies the entire 'conditional_elements_dependencies' array.

• edit.php:

      $dependent = $_POST['dependent'];
      $term =$_POST['term'];
      $dependee = $_POST['dependee'];
      $json=get_option('conditional_elements_dependencies'); // here I use syntax as specified in Omeka
      if (!$json) { $json="null"; }
      $data = json_decode($json, 1);
      $newdata = array('0'=>$dependent, '1' => $term, '2'=>$dependee);
      $data[] = $newdata;
      $json= json_encode($data);
  
  

But I need to know how to add or delete the specific data items such as dependee, term or dependent and not the entire json array.

via Chebli Mohamed