From: "David A. Black" <dblack@...>
Date: 2005-12-01T09:03:21+09:00
Subject: Re: Help constructing interesting hash?

Hi --

On Thu, 1 Dec 2005, Chris McMahon wrote:

> Suppose I have an array of arrays like
>
> [[A, B, C][1,2,3]]
>
> I can easily make a hash (using each_with_index) where one value is
> the lookup value for the other value:
>
> 1=>A
> 2=>B
> 3=>C
>
> Now suppose I have a AoA like
>
> [[A, B, C,][1,2,2]]
>
> Is there a readable way to construct a hash like
>
> 1=>[A]
> 2=>[B, C]

Here's an inject-based way:

   a.zip(b).inject({}) do |hash,(key,value)|
     (hash[value] ||= []) << key
     hash
   end


David

-- 
David A. Black
dblack@wobblini.net