Retention metric

retention.rb

ActiveRecord::Base.logger = Logger.new "/dev/null"

########################################################################################################################

class RetentionCalculation

  def users_who_bought_in_range(from, to)
    User.joins(:orders).where(
      orders: { confirmed_at: from..to }
    ).merge(Order.not_zero).merge(Order.excluding_special_users).merge(Order.not_by_salesman).pluck(:id).uniq
  end

  def users_who_bought_until(til)
    User.joins(:orders).where(
      Order.arel_table[:confirmed_at].lt(til)
    ).merge(Order.not_zero).merge(Order.excluding_special_users).merge(Order.not_by_salesman).pluck(:id).uniq
  end

  def retention_for_range(from, to)
      users_who_bought_in_range = users_who_bought_in_range(from, to)
      users_at_risk = users_who_bought_until(from)

      ((users_who_bought_in_range & users_at_risk).size.to_f / users_at_risk.size.to_f) * 100.0
  end

  def monthly_retention(month_n)
    from = Time.new(2013, month_n, 01)
    to = from + 1.month
    retention_for_range(from, to)
  end

  def average_daily_retention_for_month(month_n, year_n = Time.now.year)
    range = 30.day

    daily_data = []
    (1..Time.days_in_month(month_n, year_n)).each do |day_n|
      day = Time.new(year_n, month_n, day_n)
      daily_data << retention_for_range(day - range, day)
    end

    daily_data.sum / daily_data.size.to_f
  end

end

########################################################################################################################

class RetentionCalculationWithFakeEvents < RetentionCalculation

  def initialize(events)
    super()
    @events = events
  end

  def users_who_bought_in_range(from, to)
    users = super
    @events.each do |event_time, add_count|
      if (from..to).cover?(event_time)
        users = add_fake_users(users, add_count)
      end
    end
    users
  end

  def users_who_bought_until(til)
    users = super
    @events.each do |event_time, add_count|
      if event_time < til
        users = add_fake_users(users, add_count)
      end
    end
    users
  end

  def add_fake_users(user_id_list, add_count)
    @first_fake_id ||= User.maximum(:id) * 10
    user_id_list + (@first_fake_id..(@first_fake_id + add_count - 1)).to_a
  end

end

########################################################################################################################

puts "Month, Monthly retention, Daily retention average, (sim) Monthly retention, (sim) Daily retention average"

rc = RetentionCalculation.new
rcwfe = RetentionCalculationWithFakeEvents.new([
                                                   [Time.new(2013,2,15), 10000],
                                                   [Time.new(2013,7,15), 1000],
])

1.upto(11).each do |month|
  puts "#{month},#{rc.monthly_retention(month).round(2)},#{rc.average_daily_retention_for_month(month).round(2)},#{rcwfe.monthly_retention(month).round(2)},#{rcwfe.average_daily_retention_for_month(month).round(2)}"
end