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agarman/Shannon entropy in Clojure

Created March 10, 2017 16:29
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Shannon entropy in Clojure
(defn log2 [n] (/ (Math/log n) (Math/log 2)))
(defn entropy
"Calculate Shannon entropy for xs. Higher value is greater entropy.
Values returned between 0.0 & 8.0"
[xs]
(let [freqs (vals (frequencies xs))
cnt (reduce + freqs)
calc #(let [p (double (/ % cnt))]
(* p (log2 p)))]
(reduce - 0 (map calc freqs))))
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