M = [["a", "b"], ["c", "d"], ["e", "f"]]

x = []
...

@visits_by_day_and_hour = visits.group_by{|day| day.created_at.strftime("%Y-%m-%d")}.map {|d, items| [d, items.group_by{|hour| hour.created_at.strftime("%H")}.map{|k,v| [k, v.length]}]}

screen = [
  [9,9,4,7,4,8,9,9,9,9,2,5,6,7,8,9],
  [1,2,3,9,9,6,7,8,9,9,9,9,9,9,9,9]
...

class Item
  def raw_tag_list; "one, two, three, four, five"; end
  def public_tags; [<#Tag name=two>, <#Tag name=five>, <#Tag name=one>, <#Tag name=four>, <#Tag name=three>]; end
...

def first_day_of_month(selected_date)
...

pools = {1 => [1,2,3], 2=> [3,4,5], 3=> [5,6,7]}
intersection = []
pools.each do |k,v|
...