How to sort group_by month and year in view?

Question

pages_controller.rb

@past_challenges_by_years = @past_challenges.group_by { |t| [t.deadline.year, t.deadline.month] }

How can I break it down in the view with year and then subdivide it with month like this:

2014 # Years
 01 # Months
   Challenge
   Challenge
 02
   Challenge
 08
   Challenge
2016
 03
   Challenge
 08
   Challenge

view.html.erb

<% @past_challenges_by_years.sort.each do |year, challenges| %>
  <%= year %>
  <%= month %> # I don't know how to define this.
  <% for challenge in challenges %>
    etc...
  <% end %>
<% end %>

Answer 1

I would start by sorting the keys and then look up the challenges while iterating through those keys.

<% @past_challenges_by_years.keys.sort.each do |(year, month)| %>
  <%= year %>
  <br />
  <%= month %>
  <br />
  <% @past_challenges_by_years[[year, month]].each do |challenge| %>
    <%= challenge %>
    <br />

Edit: Here is a new solution that only displays years and months once.

@past_challenges_by_years.keys.map { |a| a[0] }.uniq.sort.each do |year|
  puts year
  @past_challenges_by_years.keys.select { |a| a[0] == year }.map { |a| a[1] }.uniq.sort.each do |month|
    puts month
    @past_challenges_by_years[[year, month]].each do |challenge|
      puts challenge
    end
  end
end

I think it should be simple enough to convert to ERB.