Synnefo » snf-ganeti

  , Statistics

  , getSumStatistics

  , getStdDevStatistics

  , getStatisticValue

  , updateStatistics

-- | Abstract type of statistical accumulations. They behave as if the given

-- statistics were computed on the list of values, but they allow a potentially

-- more efficient update of a given value.

-- For the time being, we only update the sum efficiently whereas the standard

-- deviation is recomputed on demand.

data Statistics = SumStatistics Double | StdDevStatistics [Double] deriving Show

-- | Get a statistics that sums up the values.

getSumStatistics :: [Double] -> Statistics

getSumStatistics = SumStatistics . sum

-- | Get a statistics for the standard deviation.

getStdDevStatistics :: [Double] -> Statistics

getStdDevStatistics = StdDevStatistics

-- | Obtain the value of a statistics.

getStatisticValue :: Statistics -> Double

getStatisticValue (SumStatistics s) = s

getStatisticValue (StdDevStatistics xs) = stdDev xs

-- | In a given statistics replace on value by another. This

-- will only give meaningful results, if the original value

-- was actually part of the statistics.

updateStatistics :: Statistics -> (Double, Double) -> Statistics

updateStatistics (SumStatistics s) (x, y) = SumStatistics $ s +  (y - x)

updateStatistics (StdDevStatistics xs) (x, y) =

  StdDevStatistics $ (xs \\ [x]) ++ [y]