def exclude(*args)
      args.flatten! # allow [] as a param
      args.collect!(&:to_sym) # symbolize the args
      # check respond_to? :to_sym, ActionColumns doesn't respond to to_sym
      @set.reject! { |c| c.respond_to?(:to_sym) && args.include?(c.to_sym) } # reject all items specified
    end
def exclude(*args)
      args.flatten! # allow [] as a param
      args.collect!(&:to_sym) # symbolize the args
      # check respond_to? :to_sym, ActionColumns doesn't respond to to_sym
      @set.reject! { |c| c.respond_to?(:to_sym) && args.include?(c.to_sym) } # reject all items specified
    end
the way to remove items from the set.