From: Trans <transfire@...>
Date: 2005-08-01T04:01:06+09:00
Subject: Re: QUESTION: Good data structure for list within list with duplicates?

The appropriate structure is probably Associative Arrays in Hash.

{
  "x" => [
    [ "aa", 2 ],
    [ "aa", 3 ],
    [ "bb", "boo" ],
    ...
  ],

  "y" => [
    [ "aa", 5 ],
    [ "cc" , "see" ],
    [ "cc" , "sea" ],
    ...
  ],
  ...
}

You can  create you own class for it too, start with something like
this:

  class PairHash

    def initialize()
      @outer = Hash.new([])
    end

    def add_entry( x, y, z )
      a = [y,z]
      @outer[x] << a
      a
    end

    def del_entry( x, y=nil )
      if y
        @outer[x].reject! { |e| e[0] == y }
      else
        @outer.delete(x)
      end
    end

    def inner_value?( v, x, y )
      @outer[x].select { |e| e == [y,v] }
    end

  end

  # demo
  ph = PariHash.new
  ph.add_entry( "x", "aa", 2 )
  ph.add_entry( "x", "aa", 3 )
  ph.add_entry( "x", "bb", "boo" )
  ph.inner_value?( 3, "x", "aa" ) )

T.