RFE: Enumerable#group_by, Array#^

Moin.

Here's two small RFEs. I think both of these are generally useful, but 
it feels wrong to go through the rather complex RCR process for such 
simple feature requests. If you disagree with that please let me know.


enum.group_by { |item| ... } (Enumerable#group_by):

Groups the elements of an Enumerable into a matching group. The block is 
used for mapping an item to a group.

%w(hello world ruby rocks a very lot).group_by { |word| word.size }
# => {1 => ["a"], 3 => ["lot"], 4 => ["ruby", "very"], 5 => ["rocks"]}
%w(foo bar bark qux quv).group_by { |word| word[0, 1] }
# => {"b" => ["bar", "bark"], "f" => ["foo"], "q" => ["qux", "quv"]}

files.group_by { |file| File.size(file) }
users.group_by { |user| user.age }

Ruby implementation:

module Enumerable
   def group_by
     result = Hash.new { |h, k| h[k] = Array.new }
     self.each do |item|
       group = yield(item)
       result[group] << item
     end
     return result
   end
end


ary1 ^ ary2 (Array#^):

Symmetric difference: Returns elements that are in either ary1 or ary2, 
but not in both.

[1, 2, 3] ^ [3, 4, 5] # => [1, 2, 4, 5]

Ruby implementation:

class Array
   def ^(other)
     (self - other) | (other - self)
   end
end


Comments, suggestions, notes and so on are very welcome.