From: Daniel Harple <dharple@...>
Date: 2006-03-09T01:15:48+09:00
Subject: Re: Newbie: sorting an array of custom objects

On Mar 8, 2006, at 3:48 PM, Einar H�st wrote:

> That solution requires some_field to be 'naturally' ordered,  
> though, doesn't it? (I'm very new to Ruby...) What if some_field  
> contains a string, and I want 'Oranges' to be sorted before  
> 'Apples'? Actually, I'm writing a card game, so I want 'Spades' <  
> 'Hearts' < 'Clubs' < 'Diamonds'.
>
> - Einar

As mentioned, you should use the Comparable mix-in.

class Card
   include Comparable

   SUITES = %w{Spade Heart Club Diamond}
   VALUES = %w{Ace King Queen Jack} + ("1".."10").to_a.reverse

   def initialize(suite, value)
     @suite, @value = suite, value
   end
   attr_reader :suite, :value

   def <=>(card)
     if @suite == card.suite
       VALUES.index(@value) <=> VALUES.index(card.value)
     else
       SUITES.index(@suite) <=> SUITES.index(card.suite)
     end
   end
end

and full example of a Card game skeleton:

require 'pp'

module CardGame
   class Deck
     def initialize
       @cards = []
       Card::SUITES.each do |suite|
         Card::VALUES.each { |v| @cards << Card.new(suite, v) }
       end
       # shuffle the deck
       @cards = @cards.sort_by { rand }
     end

     def draw_card
       @cards.pop
     end
   end

   class Card
     include Comparable

     SUITES = %w{Spade Heart Club Diamond}
     VALUES = %w{Ace King Queen Jack} + ("1".."10").to_a.reverse

     def initialize(suite, value)
       @suite, @value = suite, value
     end
     attr_reader :suite, :value

     def <=>(card)
       if @suite == card.suite
         VALUES.index(@value) <=> VALUES.index(card.value)
       else
         SUITES.index(@suite) <=> SUITES.index(card.suite)
       end
     end
   end

   class Hand
     def initialize
       @cards = []
     end

     def <<(card)
       @cards << card
       @cards.sort!
       @cards
     end
   end
end

deck  = CardGame::Deck.new
hand1 = CardGame::Hand.new
hand2 = CardGame::Hand.new

# Draw some cards
3.times do
   hand1 << deck.draw_card
   hand2 << deck.draw_card
end

pp hand1, hand2

__END__

-- Daniel