From: Brian Candler <B.Candler@...>
Date: 2007-02-09T00:55:53+09:00
Subject: Re: Grouping similar attributes

On Fri, Feb 09, 2007 at 12:12:42AM +0900, Dominic Son wrote:
> How would one group attributes which came from an array/db?
> 
> For example in my DB:
> 
>   ---------------------
>   |  NAME   | ETHNIC  |
>   --------------------
>   | Dominic | Asian   |
>   ---------------------
>   | John    | Asian   |
>   ---------------------
>   | Rick    | Spanish |
>   ---------------------
> 
> I'd like it to group by Ethnicity:
> 
>   Asian
>    - Dominic
>    - John
> 
>   Spanish
>    - Rich
> 
> 
> Is there some ruby thing that makes this convenient?

d = {
  'Dominic' => 'Asian',
  'John' => 'Asian',
  'Rick' => 'Spanish',
}

# Unfortunately this doesn't quite do what you want:
i = d.invert
puts i.inspect

# So:
j = Hash.new { [] }
d.each { |k,v| j[v] <<= k }
puts j.inspect