From: dblack@...
Date: 2006-03-04T05:33:54+09:00
Subject: Re: Array comparison returning nil

Hi --

On Sat, 4 Mar 2006, Logan Capaldo wrote:

>
> On Mar 3, 2006, at 1:12 PM, 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}
>> 
>> 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.
>> 
>> Julian
>> 
>> -- Posted via http://www.ruby-forum.com/.
>> 
>
> Based on join working this is my theory. One  of the two arrays have nil's in 
> it. nil.to_s is "" but nil <=> anything save  nil is nil and will cause the 
> comparision to fail.

However:

>> [1,2,nil,3].join("-")
=> "1-2--3"

so you'd get those extra -'s in one but not in the other if one but
not the other had nils.

I wonder whether the params[:itemlist] is producing strings while the
original array is integers.  That would explain join working but <=>
giving up:

irb(main):009:0> ["1","2"] <=> [1,2]
=> nil
irb(main):010:0> ["1","2"].join("-") == [1,2].join("-")
=> true


David

-- 
David A. Black (dblack@wobblini.net)
Ruby Power and Light (http://www.rubypowerandlight.com)

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