雑なエントロピーの計算

entropy.rb

str="abccddeeeeffffgggggggghhhhhhhh"

def entropy(str)
  count = str.size
  list={}
  list.default=0
  str.split("").each {|c| list[c]+=1}

  sum = 0
  list.each do |key, val|
    i = (val.to_f / count.to_f)
    sum += -(i) * Math.log(i, 2)
  end
  sum
end

e =  entropy(str)
p e, str.size * e