show.html.erb

<%= Group.timespan_filter(@range).count :conditions => :etc %>

statistics_controller.rb

		[ Phone, Plan, Group, Message ].each do |klass|
			klass.class_eval{ include TimespanFilter }
		end
	

		
		page = (params[:page] || 1).to_i - 1
		@range = case params[:scope]
		when 'day'
			e = page.days.ago.at_beginning_of_day
			s = e - 1.day
			s..e
		when 'week'
			e = page.weeks.ago.at_beginning_of_week
			s = e - 1.week
			s..e
		when 'month'
			e = page.months.ago.at_beginning_of_month
			s = e - 1.month
			s..e
		else # 'all'
			nil
		end

timespan_filter.rb

module TimespanFilter
	def self.included(base)
		base.named_scope :timespan_filter, lambda { |range|
			return {} if range.nil?

			{ :conditions => { :created_at => range } }
		}
	end
end