Collate Jekyll posts by month and year, and create both archive pages and a monthly XML feed

archivegenerator.rb

module Jekyll
  class ArchiveGenerator < Generator
    safe true

    def generate(site)
      feeddata = {}
      collate_by_month(site.posts).each do |month, posts|
        page = ArchivePage.new(site, month, posts)
        site.pages << page
        feeddata[month] = posts
      end
      	feed = MonthlyFeed.new(site, feeddata)
      	site.pages << feed
    end
 
    private
 
    def collate_by_month(posts)
      collated = {}
      posts.each do |post|
        key = "%04d/%02d" % [post.date.year, post.date.month]
        if collated.has_key? key
          collated[key] << post
        else
          collated[key] = [post]
        end
      end
      collated
    end
  end
end