Method: Array#entropy

Defined in:
lib/core/facets/array/entropy.rb

#entropy ⇒ Object

Shannon’s entropy for an array - returns the average bits per symbol required to encode the array. Lower values mean less “entropy” - i.e. less unique information in the array.

e = %w{ a b c d e e e }.entropy

("%.3f" % e)  #=> "2.128"

CREDIT: Derek


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# File 'lib/core/facets/array/entropy.rb', line 16

def entropy
  arr = self
  probHash = arr.probability
  # -- h is the Shannon entropy of the array
  h = -1.to_f * probHash.keys.inject(0.to_f) do |sum, i|
    sum + (probHash[i] * (Math.log(probHash[i])/Math.log(2.to_f)))
  end
  h
end