From: Max Muermann <ruby@...>
Date: 2006-12-07T12:46:37+09:00
Subject: [GOLF]: partitioning an array

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