I needed a Ruby Hash class that could extract a random key from the keys that have not been extracted before. Plus that the class should be re-entrant...

I found baby's class, but it was not working (at least not in Ruby 1.8.x). I made it work (slight changes), and I added the keys_not_used to make it work faster (baby's random would cycle almost forever on large lists). But I would say all credit should go to the original author, who did all the hard work.

Without further ado, here is the new version:

   1  
   2  class RandomHash < Hash 
   3  
   4     @keys_used = nil 
   5    
   6     def random_key 
   7        if @keys_used == nil then
   8           @keys_used = Hash.new 
   9        else
  10           @keys_used = Hash.new if @keys_used.size == self.size
  11        end
  12        
  13        if (@keys_used.size == 0) then
  14           pos = rand(self.size)
  15           key = self.keys[pos]
  16        else
  17           @keys_not_used = Hash.new
  18       	 self.keys.each{ |key|
  19           	if (! @keys_used.include?(key)) then
  20              	    @keys_not_used[key] = 1
  21           	end
  22  	     }
  23  	     pos = rand(@keys_not_used.size)
  24  	     key = @keys_not_used.keys[pos]
  25  	  end
  26  	  
  27        @keys_used[key] = 1
  28        return key 
  29     end 
  30  end 
  31  
  32  # Test code
  33  $sources = Hash.new
  34  $RandomSources = RandomHash.new
  35  
  36  begin
  37  
  38     (1..10).each{ |val|
  39        $sources["#{val}"] = 1
  40     }
  41     
  42     $sources.each { |src|
  43        puts "Src=#{src}"
  44        $RandomSources[src] = 1
  45     }
  46  
  47     RandomKeys = Hash.new
  48     (0..$sources.length).each{ |index| # one more than all values
  49        key = $RandomSources.random_key
  50        print "Extracted #{key} ... It's a"
  51        if (!RandomKeys.has_key?(key)) then
  52           puts " NEW key!"
  53           RandomKeys[key] = 1
  54        else
  55           puts "n OLD key!"
  56        end
  57     }
  58  end