gistfile1.rb

class UserStatistics

  # This class is responsible for aggregating User data into meaningful reports
 
 attr_accessor :user

  #
  #
  # ... snip ...
  #
  #

  # Public: Returns an aggregation of monthly spends by category
  # options is a Hash with the following keys
  #   from        -> the start date of the aggregation
  #   to          -> the end date of the aggregation
  #   categories  -> a list of categories to filter by. if ommitted, gets all categories
  # return a Hash like {2012 => {1 => {:amount => 200, :count => 2}....}....}
  def monthly_spending_by_category(options)
    by_year_and_month(
      @user.receipts.all(:date => from..to).aggregate(:date, :amount.sum, :category)
    )
  end 


private

  def by_year_and_month(array)
    array.group_by{|x| [x[0].year, x[0].month]}.map{|y| some.complicated{|l|ist comprehension } 
  end   

end