On 29 sep 2010, at 00:58, ok@cs.otago.ac.nz wrote:
Avoiding repeated additions:
movingAverage :: Int -> [Float] -> [Float] movingAverage n l = runSums (sum . take n $l) l (drop n l) where n' = fromIntegral n runSums sum (h:hs) (t:ts) = sum / n' : runSums (sum-h+t) hs ts runSums _ _ [] = []
Doaitse
I very very carefully avoided doing any such thing in my example code. For each output result, my code does two additions and one division. Yours does one addition, one subtraction, and one division, for the required case n = 3. The way I formulated it, each calculation is independent. The way you've formulated it, the error in one calculation accumulates into the next. NOT a good idea.
If this an issue then: module MovingAverage where movingAverage :: [Float] -> [Float] movingAverage (x:y:l) = movingAverage' x y l where movingAverage' x y (z:zs) = (x+y+z)/3:movingAverage' y z zs movingAverage' _ _ _ = [] movingAverage _ = [] has far fewer pattern matches, Doaitse