From: Dave Burt <dave@...>
Date: 2005-12-02T06:57:42+09:00
Subject: Re: Help constructing interesting hash?

David A. Black wrote:
>   a.zip(b).inject({}) do |hash,(key,value)|
>     (hash[value] ||= []) << key
>     hash
>   end

or, using Hash's default initializer:

hash = Hash.new {|h, k| h[k] = [] }
a.zip(b).inject(hash) do |h, (k, v)|
  h << k
end

Cheers,
Dave