Revised Ruby version from this blog post: http://blogs.sourceallies.com/2009/12/word-counts-example-in-ruby-and-scala

wordcounts.rb

rootDir = "/home/zcox/dev/20_newsgroups"
raise rootDir + " does not exist" unless File.directory? rootDir

counts = Hash.new(0) #0 will be the default value for non-existent keys
Dir["#{rootDir}/**/*"].reject{|file| File.directory? file}.each do |file|
  IO.read(file).scan(/\w+/) { |word| counts[word.downcase] += 1 }
end

open("counts-descreasing-ruby", "w") do |out|
  counts.sort { |a, b| b[1] <=> a[1] }.each { |pair| out << "#{pair[0]}\t#{pair[1]}\n" }
end

open("counts-alphabetical-ruby", "w") do |out|
  counts.sort { |a, b| a[0] <=> b[0] }.each { |pair| out << "#{pair[0]}\t#{pair[1]}\n" }
end