Micro-benchmark for new OrderedHash impl in http://github.com/rails/rails/commit/355f41d8aafd75d76db25cdda4736e0052b0605c

ordered_hash_bm.rb

# Micro-benchmark for new OrderedHash impl in http://github.com/rails/rails/commit/355f41d8aafd75d76db25cdda4736e0052b0605c
class OrderedHash < Hash
  def initialize(*args, &block)
    super
    @keys = []
  end

  def []=(key, value)
    if !has_key?(key)
      @keys << key
    end
    super
  end

  def delete(key)
    array_index = has_key?(key) && index(key)
    if array_index
      @keys.delete_at(array_index)
    end
    super
  end

  def keys
    @keys
  end

  def values
    @keys.collect { |key| self[key] }
  end

  def to_hash
    Hash.new(self)
  end

  def each_key
    @keys.each { |key| yield key }
  end

  def each_value
    @keys.each { |key| yield self[key]}
  end

  def each
    keys.each {|key| yield [key, self[key]]}
  end
end


class OrderedHashOld < Array
  def []=(key, value)
    if pair = assoc(key)
      pair.pop
      pair << value
    else
      self << [key, value]
    end
    value
  end

  def [](key)
    pair = assoc(key)
    pair ? pair.last : nil
  end

  def delete(key)
    pair = assoc(key)
    pair ? array_index = index(pair) : nil
    array_index ? delete_at(array_index).last : nil
  end

  def keys
    collect { |key, value| key }
  end

  def values
    collect { |key, value| value }
  end

  def to_hash
    returning({}) do |hash|
      each { |array| hash[array[0]] = array[1] }
    end
  end

  def has_key?(k)
    !assoc(k).nil?
  end

  alias_method :key?, :has_key?
  alias_method :include?, :has_key?
  alias_method :member?, :has_key?

  def has_value?(v)
    any? { |key, value| value == v }
  end

  alias_method :value?, :has_value?

  def each_key
    each { |key, value| yield key }
  end

  def each_value
    each { |key, value| yield value }
  end
end

module Enumerable
  def old_group_by
    assoc = OrderedHashOld.new

    each do |element|
      key = yield(element)

      if assoc.has_key?(key)
        assoc[key] << element
      else
        assoc[key] = [element]
      end
    end

    assoc
  end

  def new_group_by
    assoc = OrderedHash.new

    each do |element|
      key = yield(element)

      if assoc.has_key?(key)
        assoc[key] << element
      else
        assoc[key] = [element]
      end
    end

    assoc
  end
end

require 'benchmark'
include Benchmark
array = (1..100000).to_a

bmbm(5) do |x|
  x.report('old') do
    array.old_group_by {|i| i % 13}
  end

  x.report('new') do
    array.new_group_by {|i| i % 13}
  end
end