From: William James <w_a_x_man@...>
Date: 2006-03-04T07:58:38+09:00
Subject: Re: Array comparison returning nil

Julian Gall wrote:
> Stephen Waits wrote:
> > Maybe you could post an irb session of your own so we could see
> > what's happening?
>
> Not really possible. I am writing a Rails application with a sortable
> list on a web page. An XML_Http_request serialises the ids of the list
> items and POSTs them to my action controller. By the time I see this
> data it is an array of identifiers (numbers) in params[:itemlist].
>
> I extract this to a local array with:
>
>     new_item_ids = []
>     params[:itemlist].each {|item| new_item_ids << item}
>

new_item_ids = params[:itemlist]

> I want to compare this with another local array of my original
> (unsorted) identifiers. i.e.
>
>     original_item_ids.sort <=> new_item_ids.sort
>
> This doesn't work, although this does:
>
>     original_item_ids.sort.join('-') == new_item_ids.sort.join('-')
>
> It is odd that join works to produce the expected string where <=>
> thinks it has a problem.

See if this raises an error:
(original_item_ids + new_item_ids).sort