From: ara.t.howard@...
Date: 2006-12-07T13:25:21+09:00
Subject: Re: [GOLF]: partitioning an array

On Thu, 7 Dec 2006, Max Muermann wrote:

> Take an array of objects and partition it into subarrays, based on
> some arbitrary property of the objects. I would use this for example
> for generating a report of purchase orders and grouped by week, month,
> year, approximate value, etc.
>
> The idea is similar to Array#partition, but where partition only does
> a true/false check, the resulting array should be partitioned by the
> return value of a block so that:
>
> a = ['a','bc','def','g','hi','jkl','m']
> group(a) {|i| i.size} #=> [["a", "g", "m"], ["bc", "hi"], ["def", "jkl"]]
>
>
> My best effort so far is this:
>
> def group array, &block
> h = {}
> array.each do |e|
>   (h[yield(e)]||=[])<<e
> end
> h.to_a.map {|e| e[1] }
> end
>
> For some reason, I cannot bring myself to like this. I have the
> nagging feeling that there is a more elegant way...
>
> Cheers,
> Max

it's not a good golf solution, but here's a slightly differnet approach:

   harp:~ > cat a.rb
   module Enumerable
     def group_by &b
       h = Hash.new{|h,k| h[k] = []}
       each{|x| h[x.instance_eval(&b)] << x}
       h.values
     end
   end

   a = %w[ a bc def g hi jkl m ]
   p a.group_by{ size }


   h = { 'k' => 'v', 'K' => 'V', 'a' => 'b', 'A' => 'b' }
   p h.group_by{ first.downcase }


   harp:~ > ruby a.rb
   [["a", "g", "m"], ["bc", "hi"], ["def", "jkl"]]
   [[["K", "V"], ["k", "v"]], [["A", "b"], ["a", "b"]]]


regards.



-a
-- 
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