From: "Einar Magnús Boson" <einarmagnus@...>
Date: 2008-11-18T10:34:40+09:00
Subject: Re: function to select only certain key/value pairs from hash?


On 17.11.2008, at 23:46 , Chris Shea wrote:

> On Nov 17, 3:50 pm, Aryk Grosz <tennisbum2...@hotmail.com> wrote:
>> Whenever Im coding I usually come across having to create a new hash
>> from the key/value pairs of another hash.
>>
>> For example,
>>
>> hash = {:a => 1, :b => 2, :c => 3}
>>
>> I want to do something like this
>>
>> hash.from_keys(:a,:b) => {:a=> 1, :b=> 2}
>>
>> Is there something like this already? Perhaps in the facets  
>> library? I
>> looked and couldn't find anything.
>>
>> If anybody thinks that I shouldnt even be getting into this  
>> situation in
>> the first place, please let me know that as well.
>> --
>> Posted viahttp://www.ruby-forum.com/.
>
> Hmm... I thought there was a built in method for that.  Here's one
> way:
>
> hash = {:a => 1, :b => 2, :c => 3}
> Hash[*hash.select {|k,v| [:a,:b].include?(k)}.flatten]  #=>
> {:b=>2, :a=>1}
>
> HTH,
> Chris
>


That is ridiculously inefficient and weird :)

hash = {:a => 1, :b => 2, :c => 3}

selected = [:a, :b].map{|key|{key, hash[key]}}

p selected

# >> [{:a=>1}, {:b=>2}]




Einar Magnús Boson
+354-661 1649
einarmagnus@tistron.se
einar.boson@gmail.com