so_9333952.rb

# Benchmarking answers to http://stackoverflow.com/questions/9333952/in-ruby-how-to-make-the-string-include-method-ignore-case/9334066

# http://www.gutenberg.org/cache/epub/1661/pg1661.txt
strings = IO.read('sherlock.txt').scan(/\w+/) # 109,222 words

known = 500.times.map do
  strings.sample.downcase.chars.map{ |c| rand<0.5 ? c.upcase : c }.join
end
words = known.flat_map{ |s| [s, s+"-"] } # \w does not include -

require 'set'
require 'benchmark'
Benchmark.bm(10) do |x|
  x.report('regex'){
    words.each do |w|
      re = /\A#{w}\z/i
      strings.any?{ |s| s=~re }
    end
  }
  x.report('casecmp'){
    words.each do |w|
      strings.any?{ |s| s.casecmp(w)==0 }
    end
  }
  x.report('downarray'){
    words.each do |w|
      strings.map(&:downcase).include?(w.downcase)
    end
  }
  x.report('downonce'){
    downed = strings.map(&:downcase)
    words.each do |w|
      downed.include?(w.downcase)
    end
  }
  x.report('set_once'){
    downed = Set.new strings.map(&:downcase)
    words.each do |w|
      downed.include?(w.downcase)
    end
  }
end

#=>                 user     system      total        real
#=> regex      18.710000   0.020000  18.730000 ( 18.725266)
#=> casecmp     5.160000   0.000000   5.160000 (  5.155496)
#=> downarray  16.760000   0.030000  16.790000 ( 16.809063)
#=> downonce    0.650000   0.000000   0.650000 (  0.643165)
#=> setonce     0.040000   0.000000   0.040000 (  0.038955)