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danbst/entropy.hs

Created February 8, 2016 13:08
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Entropy of a list
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entropy.hs
import Data.Char
import Data.Map (Map)
import qualified Data.Map as Map
entropy :: (Ord a) => [a] -> Float
entropy dta =
let freqmap = Map.fromListWith (+) $ zip dta (repeat 1)
modifier = 1.0 / fromIntegral (length dta)
freqs = Map.map (\v -> fromIntegral v * modifier) freqmap
log2 n = log n / log 2.0
in Map.fold (\p acc -> acc - p * log2 p) 0.0 freqs
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