sigma rejection algorithm - returns average of values that are not too far from average

sigmaRejection.hs

import Data.List

sigmaRejection = sigmaRejection' 3

sigmaRejection' distance xs =
  mean $ filter (\x-> abs(mean xs - x) < distance * sigma) xs
 where
  mean xs = realToFrac (sum xs) / (genericLength xs)
  sigma = sqrt $ ((sum xs)^2 - (sum $ map (^2) xs)) / genericLength xs