Sort an array based on an attribute of its objects

[josh]

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:

• Request:
  • Object 1
  • Object 3
• Cancelled:
  • Object 2
... and so on...

What’s an elegant way to do this?

Thanks a lot,
Josh

[josh]

Hi –

On Thu, 28 Aug 2008, Joshua M. wrote:

I need this because I want then to iterate through the hash and display

Cancelled:

• Object 2

... and so on...

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

[josh]

On Thu, Aug 28, 2008 at 1:58 PM, David A. Black [email protected]
wrote:
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

–
http://ruby-smalltalk.blogspot.com/

There’s no one thing that’s true. It’s all true.

[josh]

On Thu, Aug 28, 2008 at 1:39 PM, Joshua M. [email protected] wrote:

{status1 => [obj1, obj3],
status3 => [obj2],
status4 => [obj4]}

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