From: Mark Hubbart <discord@...>
Date: 2004-04-24T19:22:08+09:00
Subject: Re: Array to Hash


On Apr 24, 2004, at 2:54 AM, Pe�a, Botp wrote:

>
> Robert Klemme [mailto:bob.news@gmx.net] wrote:
>
>> There's one reason why this may not be a standard method:
>> there are at least two equally reasonable representations of
>> a mapping stored in an array:
>>
>> Nested arrays as returned by Hash#to_a: [[key1, val1], [key2, val2]]
>>
>> A sequence: [key1, val1, key2, val2] as used by Hash[]
>>
>> Obviously there is no simple way from a Hash to an Array and
>> back to a Hash.
>> (Btw: is that ever needed? I mean, if you have a hash you can
>> easily create a copy without an intermediate array.)
>>
>> So the question is wich representation Enumerable#to_h should
>> expect - nested or sequence?
>
> I am concerned more on the language.
>
> Which would you prefer?
>
> Hash#to_a or Hash[*mumblearray.flatten]
>
> IMHO, I prefer the first; more rubyish. The second looks weird, and my 
> brain
> aches just to remember it.
>
> Now, since the first notation returns an array of pairs, then _it_ is 
> in
> consonance with the hash notation (since hashes are pairs too). Ergo, 
> to
> answer your question, I choose the nested.
>
> Ok, now I have a question for you robert (since you're one of the ruby 
> gurus
> here), Is it possible for #to_h to determine if the array is nested or 
> not,
> and then adjust accordingly?

Well, I'm not robert :) but here's one way to check. If the array 
consists of objects that respond to #size and #inject, and #size 
returns 2, it is assumed that this is a nested array. Otherwise, it 
runs it through the Hash[obj] thing.


class Array
   def to_h
     if all?{|e| e.respond_to?(:size, :inject) and e.size == 2}
       inject({}){|h,(k,v)| h[k] = v; h}
     else
       Hash[*self]
     end
   end
end


--Mark


>>     robert
>
> kind regards -botp
>