def matrix_for(collection,row_attribute,col_attribute,display_attribute)
    returnstring = "<table>\n"
    returnstring += ([" <tr>\n  <td>\n"] + entries_for(collection,col_attribute)).join("\n  </td>\n  <td>\n") + "\n  </td>\n </tr>\n"
    entries_for(collection,row_attribute).each do |row|
      r = [" <tr>\n  <td>\n#{row}"]
      entries_for(collection,col_attribute).each do |column|
        r << collection.select{|p| p.send(col_attribute) == column && p.send(row_attribute) == row}.map{|p| p.send(display_attribute)}.join("<br/>\n")
      end
      returnstring += r.join("\n  </td>\n  <td>") + "\n  </td>\n </tr>\n"
    end
    returnstring + "</table>"
  end