From: Gennady Bystritsky <Gennady.Bystritsky@...>
Date: 2007-10-30T02:04:33+09:00
Subject: Re: Something wrong with my hash of hash

list-bounce@example.com wrote:
> I try to get a hash of hash to make some sort of counter (I have a set
> of random pair and want to count the number of times they
> appear). I use
> this code but even if I can access data, my hash seems empty (so each
> and the others don't work):
>
>
> h = Hash.new(Hash.new(0))
> h["a"]["b"] += 1
> h["a"]["b"] += 1
> h["a"]["c"] += 1
> p h["a"]["b"]  => 2
> p h["a"]["c"]  => 1
> p h.class  => Hash
> p h["a"].class  => Hash
> p h["a"]["b"].class  => Fixnum
> p h  => {}
>
>
> What's wrong?
>
> Lars

Try this definition:

h = Hash.new { |h, k|
  h[k] = Hash.new(0)
}

It will actually modify 'h' rather than simply returning and modifying the default value.

Gennady.