word_frequency.rb

class WordFrequency

  def initialize(words)
    @words = words.split(/\W+/)
  end

  def get_frequency
    h = Hash.new(0)
    @words.each do |w|
      h[w] += 1
    end
    return h
  end

  def top_words(n)
    get_frequency.sort_by { |key, value| value }.reverse[0..n-1]
  end

end

require 'benchmark' 

time = Benchmark.measure do 
  RANDOM_WORDS = %w[something absolutely computer what can watch understand lose water magic words believe structure really different help meaning cell chip driver cup wheel]
  word_arrays = []
  word_arays = 1500000.times { word_arrays << RANDOM_WORDS.sample }
  words = word_arrays.join(" ")
  freq = WordFrequency.new(words)
  p freq.top_words(5)
end
puts time
#  2.070000   0.040000   2.110000 (  2.123516)