From: Morton Goldberg <m_goldberg@...>
Date: 2007-10-21T08:17:12+09:00
Subject: Re: What's the ruby way of grouping elements of an array?

On Oct 19, 2007, at 9:05 PM, William James wrote:

> On Oct 19, 2:01 pm, Sam Kong <sam.s.k...@gmail.com> wrote:
>> I thought this would be a common need but I couldn't find a method.
>>
>> Let's say I have an array of objects. I want to group the elements  
>> by a property of objects.
>>
>> people.group_by do |person|
>>   person.age
>> end
>>
>> The above method should return an array of arrays grouped by age.
>>
>> What's the ruby way for this case? I think I can implement it but  
>> I am sure that a good way already exists.
>
> It's pretty simple.
>
> class Array
>   def group_by
>     h = Hash.new{ [] }
>     each{|x|
>       h[ yield( x ) ] += [ x ]
>     }
>     h.values
>   end
> end

That's good, but I think the  following modification makes it a  
little better:

<code>
class Array
    def group_by
       h = Hash.new { |h, k| h[k] = [] }
       each { |item| h[yield(item)] << item }
       h.values
    end
end
</code>

Regards, Morton