From: "F. Senault" <fred@...>
Date: 2009-01-15T07:39:05+09:00
Subject: Re: a beginner case question

Le 14 janvier 2009 � 16:56, Taylor Strait a �crit :

> This does not because of the return statements.  However, I need to
> reverse the result for those two options.  How can I do this with case
> statements?  Or must I use if..elsif?

To go a step further than just answering your question, I'd refactor the
whole function like this :

def single_choice(object)
  l = case object.list_method
      when /^position/ then lambda { |x| x.position }
      when /^rand/     then lambda {     rand       }
      when /^alpha/    then lambda { |x| x.to_s     }
      when /^length/   then lambda { |x| x.length   }
      end
  sorted_answers = object.answers.sort_by(&l)
  if order =~ /desc$/
    sorted_answers.reverse!
  end
  sorted_answers
end

The lamba is there to avoid the repetition of the sort_by calls, the use
of regexpen means you have to standardize your methods (length and
length_desc vs shortest_firts and longest_first).  On the other hand,
you can manage all kind of sorts without duplicating your sort method.

An even nicer form, if your arrays are of a manageable size, would be :

def single_choice(object)
  r = (object.list_method =~ /desc/ ? -1 : 1)
  l = case object.list_method
      when /^position/ then lambda { |x, y| (x.position <=> y.position) * r }
      when /^rand/     then lambda {        rand                            }
      when /^alpha/    then lambda { |x, y| (x.to_s <=> y.to_s)         * r }
      when /^length/   then lambda { |x, y| (x.length <=> y.length)     * r }
      end
  object.answers.sort(&l)
end

(But sort is slower for big arrays.)

You can also extract the case expression into a helper method if you
need to sort other kinds of objects...

HTH,

Fred
-- 
"- Anyway, United Amalgamated Consolidated Holdings probablt don't worry
about that sort of thing.  They've probabbly got a Vice-President in
Charge of Being Cursed.  - And he probably gets his secretary to deal
with it."                         (Terry Pratchett, Johnny and the Dead)