```ruby
module Feedcellar
  class GroongaSearcher
    class << self
      def search(database, words, options)
        feeds = database.feeds
        feeds = feeds.select do |feed|
          expression = nil
          words.each do |word|
            sub_expression = (feed.title =~ word) |
                             (feed.description =~ word)
            if expression.nil?
              expression = sub_expression
            else
              expression &= sub_expression
            end
          end

          if options[:mtime]
            base_date = (Time.now - (options[:mtime] * 60 * 60 * 24))
            mtime_expression = feed.date > base_date
            if expression.nil?
              expression = mtime_expression
            else
              expression &= mtime_expression
            end
          end

          if options[:resource]
            resource_expression = feed.resource =~ options[:resource]
            if expression.nil?
              expression = resource_expression
            else
              expression &= resource_expression
            end
          end

          expression
        end

        order = options[:reverse] ? "ascending" : "descending"
        sorted_feeds = feeds.sort([{:key => "date", :order => order}])

        sorted_feeds
      end

      def latest(database)
        latest_feeds = []

        feeds = database.feeds
        # TODO: I want to use the groonga method for grouping.
        feeds.group_by {|feed| feed.resource.xmlUrl }.each do |url, group|
          latest_feed = group.sort_by {|feed| feed.date }.last
          next unless latest_feed
          next unless latest_feed.title
          latest_feeds << latest_feed
        end

        latest_feeds
      end
    end
  end
end
```

Use rroonga method for latest grouping
user
```ruby
module Feedcellar
  class GroongaSearcher
    class << self
      def search(database, words, options)
        feeds = database.feeds
        feeds = feeds.select do |feed|
          expression = nil
          words.each do |word|
            sub_expression = (feed.title =~ word) |
                             (feed.description =~ word)
            if expression.nil?
              expression = sub_expression
            else
              expression &= sub_expression
            end
          end

          if options[:mtime]
            base_date = (Time.now - (options[:mtime] * 60 * 60 * 24))
            mtime_expression = feed.date > base_date
            if expression.nil?
              expression = mtime_expression
            else
              expression &= mtime_expression
            end
          end

          if options[:resource]
            resource_expression = feed.resource =~ options[:resource]
            if expression.nil?
              expression = resource_expression
            else
              expression &= resource_expression
            end
          end

          expression
        end

        order = options[:reverse] ? "ascending" : "descending"
        sorted_feeds = feeds.sort([{:key => "date", :order => order}])

        sorted_feeds
      end

      def latest(database)
        latest_feeds = []

        feeds = database.feeds
        feeds.group("resource.xmlUrl", :max_n_sub_records => 1).each do |group|
          latest_feed = group.sub_records[0]
          next unless latest_feed
          next unless latest_feed.title
          latest_feeds << latest_feed
        end

        latest_feeds
      end
    end
  end
end
```
assistant