Grouping by year

shit_grouper.rb

module ShitGrouper
  def self.group(array)
    array.group_by(&:year)
  end

  def self.ungroup(hash)
    hash.values.flatten
  end
end

class Shit
  attr_reader :year, :weight

  def initialize(year, weight)
    @year = year
    @weight = weight
  end
end

shits = 10.times.map do |n|
  Shit.new(2000 + n, rand(10..100))
end

grouped_shit = ShitGrouper.group(shits)
ungrouped_shit = ShitGrouper.ungroup(grouped_shit)

if ungrouped_shit == shits
  puts "I'm still the same shit as I used to be"
end