From: Robert Klemme <bob.news@...>
Date: 2004-06-25T01:53:07+09:00
Subject: Re: N Dimensional Hash?


"Jim Freeze" <jim@freeze.org> schrieb im Newsbeitrag
news:20040624134324.GA33615@freeze.org...
> Hi
>
> I'm looking for an object that behaves like a
> n-dimensional hash. We'll start with two dimensions
> to make this easy.
>
> Lets say I have the data table
>
>  [
>    %w{mini cooper   red},
>    %w{ford focus    white},
>    %w{ford mustang  blue},
>    %w{ab   cd       1},
>    %w{abc  d        2},
>    %w{a    bcd      3},
>  ]
>
> Obviously I could build hash with:
>
>   h = { "mini" => {},
>         "ford" => {},
>         "ab"   => {},
>         "abc"  => {},
>         "a"    => {}
>       }
>
>   h["mini"] = { "cooper" => "red" }
>   h["ford"] = { "focus" => "white", "mustang" => "blue" }
>   h["ab"]   = { "cd" => 1 }
>   h["abc"]  = { "d" => 2 }
>   h["a"]    = { "bcd" => 3 }
>
> But this is painful.
> Before I go and write a class to do this, is there
> something that already does this. Like, maybe tuples,
> which I don't understand.
>
> ..Hmm, I would describe this as a hierarchal struct with
> named arguments.
>
>  h[:make=>"mini", :model=>"cooper"] #=> "red"
>  sames as:
>  h[:model=>"cooper", :make=>"mini"] #=> "red"

The typical idiom is:

ins = lambda {|h,k| h[k] = Hash.new &ins}
h = Hash.new &ins

like in

>> ins = lambda {|h,k| h[k] = Hash.new &ins}
=> #<Proc:0x10187298@(irb):1>
>> h=Hash.new &ins
=> {}
>> h["foo"]
=> {}
>> h["foo"]["bar"]
=> {}
>> h
=> {"foo"=>{"bar"=>{}}}
>> h["bar"]["test"] = "val"
=> "val"
>> h
=> {"foo"=>{"bar"=>{}}, "bar"=>{"test"=>"val"}}

Alternatively you can use Arrays as hash keys.  But that depends on your
requirements.

Kind regards

    robert