From: Ross Bamford <rosco@...>
Date: 2006-12-07T17:50:10+09:00
Subject: Re: [GOLF]: partitioning an array

On Thu, 07 Dec 2006 03:46:37 -0000, Max Muermann <ruby@muermann.org> 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...
>

Maybe:

a = ['a','bc','def','g','hi','jkl','m']
# => ["a", "bc", "def", "g", "hi", "jkl", "m"]

a.inject([]){|dst,e|(dst[e.length-1]||=[])<<e;dst}
# => [["a", "g", "m"], ["bc", "hi"], ["def", "jkl"]]



-- 
Ross Bamford - rosco@roscopeco.remove.co.uk