test_sorting.rb

#!/usr/bin/ruby
#
# Testing whether sorting then reversing is faster than sorting "the right way".
# Short answer: sort/reverse are written in C, your own sort function will be written in Ruby.

require 'benchmark'

n = 1_000

ids = (0..10_000).to_a.sort_by { rand }

#               user     system      total        real
# sort.reverse  2.510000   0.150000   2.660000 (  2.904603)
Benchmark.bm do |x|
  x.report("sort.reverse") { n.times do ; ids.sort.reverse ; end }
end

#             user     system      total        real
# sort method 81.090000   0.790000  81.880000 ( 85.358657)
Benchmark.bm do |x|
  x.report("sort method") { n.times do ; ids.sort {|a,b| b <=> a} ; end }
end