def delete_at index
      @data.delete_at @index[index]
      @index = Daru::Index.new(@index.to_a - [index])

      update_position_cache
    end
def delete_at index
      @data.delete_at @index[index]
      @index = Daru::Index.new(@index.to_a - [index])

      update_position_cache
    end
Delete element by index