standardDeviation :: Floating a => [a] -> a
standardDeviation xs = sqrt $ mean squareDiffs
  where
    meanValue   = mean xs
    squareDiffs = map (\x -> x*x) $ map (meanValue -) xs
standardDeviation :: Floating a => [a] -> a
standardDeviation xs = sqrt $ mean squareDiffs
  where
    meanValue   = mean xs
    squareDiffs = map (\x -> x*x) $ map (meanValue -) xs
standardDeviation xs = sqrt $ mean squareDiffs
  where
    meanValue   = mean xs
    squareDiffs = map (\x -> x*x) $ map (meanValue -) xs