Using group_by on arrays

group_by.rb

class Post

	attr_reader :date, :text

	def initialize(text)
		@date = "2010-10-#{rand(2)+1}"
		@text = text
	end
end

posts = []
10.times do |t|
	posts << Post.new("text no. #{t}")
end

posts_grouped_by_date = posts.group_by(&:date)
posts_grouped_by_date.keys #=>["2010-10-1", "2010-10-2"]
posts_grouped_by_date['2010-10-1'].size #=>3
posts_grouped_by_date['2010-10-2'].size #=>7