Ruby function, calculates the shannon entropy for a given word

gistfile1.rb

def word_entropy(word)
  len = word.chars.count.to_f
  log2 = Math.log(2)
  
  counts = word.chars.inject({}) do |h,c|
    h[c] = (h[c] || 0) + 1
    h
  end

  counts.inject(0) do |entropy, pair|
    frequency = (pair[1] / len)
    entropy = (frequency * (Math.log(frequency) / log2))
  end.abs
end

if __FILE__ == $0
  $KCODE = "UTF8"
  require 'rubygems'
  require 'benchmark'
  require 'active_support'

  puts "Examples:"
  words = ["aba17a8c1041b4b4", "gR~_'UJ78KOl:yNp",
           "aaaaaaaaaaaaaaaa", "password", "blërg"]

  words.each do |w|
    puts 'word_entropy("%s") #=> %f' % [w, word_entropy(w)]
  end

  puts "\nBenchmarks:"
  n = 10000
  Benchmark.bm do |x|
    x.report('word_entropy("aba17a8c1041b4b4"): ') { n.times { word_entropy("aba17a8c1041b4b4") }}
    x.report('word_entropy("gR~_\'UJ78KOl:yNp"): ') { n.times { word_entropy("gR~_'UJ78KOl:yNp") }}
    x.report('word_entropy("aaaaaaaaaaaaaaaa"): ') { n.times { word_entropy("aaaaaaaaaaaaaaaa") }}
  end
end