examples/rosettacode/entropy.nit

   1 #!/usr/bin/env nit
   2 #
   3 # This file is part of NIT ( http://www.nitlanguage.org ).
   4 # This program is public domain
   5
   6 # Task: Entropy
   7 # SEE: <http://rosettacode.org/wiki/Entropy>
   8 module entropy
   9
  10 import counter
  11
  12 # Basic implementation with a hashmap of chars to count them
  13 fun entropy(string: String): Float
  14 do
  15         var cpt = new HashMap[Char, Int]
  16         for char in string.chars do
  17                 var occ = cpt.get_or_default(char, 0)
  18                 cpt[char] = occ + 1
  19         end
  20
  21         var len = string.length.to_f
  22         var e = 0.0
  23         for char, occ in cpt do
  24                 var freq = occ.to_f / len
  25                 e = e - freq * freq.log_base(2.0)
  26         end
  27         return e
  28 end
  29 print entropy("1223334444")
  30
  31 # Alternative one-liner implementation using the `Counter::entropy` method of the library `counter`
  32 print "1223334444".chars.to_counter.entropy