sort_by_category.rb

def articles_list
  articles = @items.select { |i| i.path.match(/reading_room\/.+/) unless i.path.nil? }

  articles_by_category = {}
  # organize by category
  articles.each do |article|
    articles_by_category[article[:category]] ||= []
    articles_by_category[article[:category]].push article
  end

  # return sorted articles by sorted categories
  articles_by_category.sort.map do |category, articles|
    %{
      <h1>#{category}</h1>
      #{ articles.sort_by{|a| a[:title] }.map { |a| article_preview a }.join '' }
    }
  end.join ''
end