From: "David A. Black" <dblack@...>
Date: 2008-08-28T20:58:58+09:00
Subject: Re: Sort an array based on an attribute of its objects

Hi --

On Thu, 28 Aug 2008, Joshua Muheim wrote:

> Hi all
>
> The title of this topic is not very good, but I didn't really know how
> to describe it in just a few words...
>
> So here is what I need to do:
>
> I have a array of some objects:
>
> [obj1, obj2, obj3, obj4]
>
> All objects have a method "status" that returns a status object, like
> "open", "request", "cancelled", "completed" etc.
>
> Now I'd like to sort the elements after theses statuses into a new hash,
> so in the end it should look something like this:
>
> {status1 => [obj1, obj3],
> status3 => [obj2],
> status4 => [obj4]}
>
> I need this because I want then to iterate through the hash and display
> an HTML list grouped by status:
>
> <ul>
>  <li>
>    Request:
>    <ul>
>      <li>Object 1</li>
>      <li>Object 3</li>
>    </ul>
>  </li>
>  <li>
>    Cancelled:
>    <ul>
>      <li>Object 2</li>
>    </ul>
>  </li>
>  ... and so on...
> </ul>
>
> What's an elegant way to do this? :-)

In Ruby 1.9 you can do:

   array.group_by {|obj| obj.status }

and get a hash. If you need to roll your own:

   class Array
     def group_by
       hash = Hash.new {|h,k| h[k] = [] }
       each {|e| hash[yield(e)] << e }
       hash
     end
   end

(or in a module, or whatever).


David

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