From: Rob Biedenharn <Rob@...>
Date: 2011-07-16T04:47:54+09:00
Subject: Re: Comparing hashes based on their keys

On Jul 15, 2011, at 3:01 PM, Stefano Mioli wrote:

> On 7/15/11 7:18 PM, Rob Biedenharn wrote:
>
> class Hash
>  def same_key_structure?(other)
>    return false unless other.is_a?(Hash)
>    return false unless self.keys == other.keys && self.keys.all?{|_| 
> _.is_a?(Symbol)}
>    self.keys.all? {|_|self[_].is_a?(Hash) ?  
> self[_].same_key_structure?(other[_]) : !other[_].is_a?(Hash)}
>  end
> end
>
>
> Now that I think about it, that
>
> 	self.keys == other.keys
>
> might cause problems, because I didn't specify (sorry, my bad) that  
> I don't care about which order the keys appear in.
>
> In other words, I consider these two hashes to be equal:
>
> 	h1 = {:x => nil, :y => nil}
> 	h2 = {:y => nil, :x => nil}
>
> but h1.keys == h2.keys would return false in this context.

   then sort them:

   return false unless self.keys.sort == other.keys.sort

Since they are Hashes, I'd certainly hope that the order of the keys  
didn't matter. ;-)

I should have realized that particularly since 1.9.2's Hashes return  
their keys in an order dependent on their insertion to the Hash. (And  
I gave a talk to the Cincinnati Ruby Brigade just last month about  
differences between 1.8.6 and 1.9.2 that included this fact.)

-Rob

>
> Array could probably benefit from something like RSpec's '=~' to  
> test arrays for equality regardless of the order of their elements,  
> wouldn't it?
> That is, unless I'm missing some existing method that does that.
>
> -- 
> Stefano Mioli
>

Rob Biedenharn		
Rob@AgileConsultingLLC.com	http://AgileConsultingLLC.com/
rab@GaslightSoftware.com		http://GaslightSoftware.com/