public void toggleDataSetSelected(int index)
  {
    // Itereer door dataset/category/subcategory
    for (DataSet set: this.datasets)
    {
      if (set.id == index)
      {
        // toggle alles hieronder
        for (Category cat: set.categories)
        {
          for (SubCategory scat: cat.subcategories)
          {
            scat.selected = !scat.selected;
          }
        }
      }
      else
      {
        // Ga dieper kijken
        for (Category cat: set.categories)
        {
          if (cat.id == index)
          {
            for (SubCategory scat: cat.subcategories)
            {
              scat.selected = !scat.selected;
            }
          }
          else
          {
            // Dieper
            for (SubCategory scat: cat.subcategories)
            {
              if (scat.id == index)
              {
                scat.selected = !scat.selected;
              }
            }
          }
        }
      }
    }
  }