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{-# LANGUAGE FlexibleInstances #-}
{- Copyright 2016 Joey Hess <id@joeyh.name>
-
- Licensed under the GNU AGPL version 3 or higher.
-}
module Entropy where
import Data.List
import qualified Data.ByteString.UTF8 as B
class ToChars t where
toChars :: t -> [Char]
instance ToChars String where
toChars = id
instance ToChars B.ByteString where
toChars = B.toString
shannonEntropy :: ToChars s => s -> Double
shannonEntropy = sum . map lg' . fq' . map (fromIntegral.length) . group . sort . toChars
where
lg' c = (c * ) . logBase 2 $ 1.0 / c
fq' c = let sc = sum c in map (/ sc) c
totalEntropy :: ToChars s => s -> Double
totalEntropy s = shannonEntropy s * fromIntegral (length (toChars s))
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