The great TR vs GSUB battle

benchmark.rb

require 'benchmark'

def vowel_cipher(string)
  string.tr "aAeEiIoOuU", "eEiIoOuUaA"
end

NEXT_VOWEL = {"a"=>"e", "A"=>"E", "e"=>"i", "E"=>"I", "i"=>"o",
              "I"=>"O", "o"=>"u", "O"=>"U", "u"=>"a", "U"=>"A"}

def vowel_cipher_gsub(str)
  str.gsub(/[aeiou]/i, NEXT_VOWEL)
end

Benchmark.bm do |x|
  x.report { 1000000.times {  vowel_cipher("Paper Cup") } }
  x.report { 1000000.times {  vowel_cipher_gsub("Paper Cup") } }
end

results.txt

       user     system      total        real
   2.871711   0.000000   2.871711 (  3.027596)
   5.298556   0.000000   5.298556 (  5.449371)