# coding: utf-8
require 'active_support/core_ext/string/conversions.rb'
require 'benchmark/ips'

data = ([
  '11/15/2015',
  '11/29/2015',
  '11/11/2015',
  '11/5/2015',
  '11/18/2015',
  '11/1/2015',
  '11/11/2015',
  '11/30/2015',
  '11/6/2015',
  '11/4/2015'
] * 1000).shuffle

def naive_sort(ary)
  ary.sort { |a, b| Time.strptime(b, '%m/%d/%Y') <=> Time.strptime(a, '%m/%d/%Y') }
end

def sort_by(ary)
  ary.sort_by { |x| Time.strptime(x, '%m/%d/%Y') }.reverse
end

Benchmark.ips do |x|
  x.report('sort by')  { sort_by(data) }
  x.report('naive') { naive_sort(data) }

  x.compare!
end

__END__
% ruby benchmarks.rb

Warming up --------------------------------------
           sort by     1.000  i/100ms
           naive     1.000  i/100ms
Calculating -------------------------------------
            sort by      9.721  (± 0.0%) i/s -     49.000  in   5.045643s
            naive      2.228  (± 0.0%) i/s -     12.000  in   5.390025s

Comparison:
            sort by:        9.7 i/s
            naive:        2.2 i/s - 4.36x slower