base_report_aggregator.rb

  def recurse_grouping(grouping, by, f, grouped_values = {})
    key = by.shift
    grouping.map do |name,group|
      grouped_values[key] = name
      if by.empty?
        data = group.data.first.to_hash.merge(grouped_values)
        f.call(group, data)
      else
        recurse_grouping(grouping / name, by.dup, f, grouped_values.dup)
      end
    end.flatten
  end