From: James Edward Gray II <james@...>
Date: 2007-02-09T01:59:29+09:00
Subject: Re: Grouping similar attributes

On Feb 8, 2007, at 9:12 AM, 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

Here's one idea:

 >> Person = Struct.new(:name, :ethnic)
=> Person
 >> people = [Person.new("Dominic", "Asian"), Person.new("John",  
"Asian"), Person.new("Rick, "Spanish")]
^C
 >> people = [Person.new("Dominic", "Asian"), Person.new("John",  
"Asian"), Person.new("Rick", "Spanish")]
=> [#<struct Person name="Dominic", ethnic="Asian">, #<struct Person  
name="John", ethnic="Asian">, #<struct Person name="Rick",  
ethnic="Spanish">]
 >> by_ethnic = Hash.new
=> {}
 >> people.each do |person|
?>   (by_ethnic[person.ethnic] ||= Array.new) << person
 >> end
=> [#<struct Person name="Dominic", ethnic="Asian">, #<struct Person  
name="John", ethnic="Asian">, #<struct Person name="Rick",  
ethnic="Spanish">]
 >> by_ethnic
=> {"Asian"=>[#<struct Person name="Dominic", ethnic="Asian">,  
#<struct Person name="John", ethnic="Asian">], "Spanish"=>[#<struct  
Person name="Rick", ethnic="Spanish">]}

Hope that helps.

James Edward Gray II