How to add order by in select query in rails 2.1.1

How can I add order by birthdate desc to the following query?

User have friends 
User have profile

   now = Date.today
   end = now + 7.days

u= User.find(id)
@somevariable = u.friends.select{|f|
      date = f.profile.birthdate开发者_JAVA技巧 if f.profile
      selected = false
      if date
 if (now.month == date.month) && (date.day >= now.day && date.day <= end_day.day )
          selected =true
        elsif (end.month == date.month) && (date.day <= end.day && end_day.month != today.month)
          selected = true
        else
          selected=false
        end
       end
      selected }

Everything is working fine, except I need to order the results by birthdate.

The really lazy way to do this is to slap a #sort_by on the end - however, I would NOT. If you fix your code, then I might be able to order by during the initial find - however as is, it is unreadable.