From: Ross Bamford <rosco@...>
Date: 2005-12-01T07:22:31+09:00
Subject: Re: Help constructing interesting hash?

On Wed, 30 Nov 2005 21:57:00 -0000, Chris McMahon  
<christopher.mcmahon@gmail.com> 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]
>
> ?
>
> Thanks,
> -Chris
>

I assumed you meant [['A', 'B', 'C'],[1,2,2]] - I know comma at end can be  
valid syntax but not sure if it fits here?
If so, this seems to work:

a = [['A', 'B', 'C'],[1,2,2]]

h = {}
a[1].each_with_index { |it, i|
   (h[it] ||= []) << a[0][i]
}

p h  # => {1=>["A"], 2=>["B", "C"]}

-- 
Ross Bamford - rosco@roscopeco.remove.co.uk