From: Robert Klemme <bob.news@...>
Date: 2004-06-25T16:38:05+09:00
Subject: Re: N Dimensional Hash?


"Shashank Date" <sdate@everestkc.net> schrieb im Newsbeitrag
news:2k0g6fF15rigjU1@uni-berlin.de...
>
> "Robert Klemme" <bob.news@gmx.net> wrote in message
>
> > Alternatively you can use Arrays as hash keys.
>
> I always thought that Arrays cannot be used as hash keys,
> but after reading your email and re-reading Pickaxe (pg. 207)
> I learnt that you _can_ use them albeit with a little
> inconvenience: that you have to call Hash#rehash method
> to reindex the hash whenever a key hash changes.

You should consider hash keys as constants.  You can even enforce that by
inserting a frozen copy but that's not needed.  Just don't reuse the
instance after you put it into the hash:

# arrays as keys
hash={}

[
   %w{mini cooper   red},
   %w{ford focus    white},
   %w{ford mustang  blue},
   %w{ab   cd       1},
   %w{abc  d        2},
   %w{a    bcd      3},
].each do |a|
  hash[a] = a.pop
end

p hash
p hash[%w{ford focus}]


# hash of hashes
i=lambda {|h,k| h[k] = Hash.new &i}
hash = Hash.new &i

[
   %w{mini cooper   red},
   %w{ford focus    white},
   %w{ford mustang  blue},
   %w{ab   cd       1},
   %w{abc  d        2},
   %w{a    bcd      3},
].each do |a|
  val = a.pop
  key = a.pop
  a.inject(hash) {|h,k| h[k]}[key] = val
end

p hash
p hash["ford"]["focus"]


Kind regards

    robert