nilspore

(defn entropy
  "Calculate the Shannon entropy, a.k.a. amount of information, in a
  distribution. Uses the log-base-2 version, so the result can be thought of as
  the number of bits of information. Accepts either a seq of numbers or a map of
  freqencies like that returned by the `clojure.core/freqencies` function.
  Ex:
    (entropy [1])          ; => 0.0
    (entropy [0 1 0 1])    ; => 1.0
    (entropy [0 1 2 3])    ; => 2.0
    (entropy {0 2, 1 2})   ; => 1.0