Sort an array based on an attribute of its objects

ruby-talk
1

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? :slight_smile:

Thanks a lot,
Josh

···

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Posted via http://www.ruby-forum.com/.

2

Hi --

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? :slight_smile:

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

···

On Thu, 28 Aug 2008, Joshua Muheim wrote:

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3

If working with a Set is fine (there's #to_set) that's provided by Set#classify.

···

On Thu, Aug 28, 2008 at 1:39 PM, Joshua Muheim <forum@josh.ch> wrote:

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]}

4

David beat me to the line, but as somebody will post an inject based
solution anyway, why not let it be me ;).

class Array
   def group_by message = nil
     inject( Hash.new {|h,k| h[k] = [] } ){ |h, e|
       h[message ? e.send( message ) : yield(e)] << e
       h
     }
   end
end

p %w{ Hello Brave GNU World }.group_by {|o| o.size }
p %w{ Hello Brave GNU World }.group_by( :size )

Cheers
Robert

···

On Thu, Aug 28, 2008 at 1:58 PM, David A. Black <dblack@rubypal.com> wrote:

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