{-
Copyright (C) 2011 Dr. Alistair Ward
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see .
-}
{- |
[@AUTHOR@] Dr. Alistair Ward
[@DESCRIPTION@] Miscellaneous statistics functions.
-}
module Factory.Math.Statistics(
-- * Functions
getMean,
getWeightedMean,
-- getDispersionFromMean,
getVariance,
getStandardDeviation,
getAverageAbsoluteDeviation,
getCoefficientOfVariance,
nCr,
nPr
) where
import Control.Arrow((***))
import Control.Parallel(par, pseq)
import qualified Data.Foldable
import qualified Data.List
import qualified Factory.Math.Factorial as Math.Factorial
import qualified Factory.Math.Implementations.Factorial as Math.Implementations.Factorial
import qualified Factory.Math.Power as Math.Power
{- |
* Determines the /mean/ of the specified numbers; .
* Should the caller define the result-type as 'Rational', then it will be free from rounding-errors.
-}
getMean :: (
Data.Foldable.Foldable foldable,
Fractional result,
Real value
)
=> foldable value
-> result
getMean foldable
| denominator == 0 = error "Factory.Math.Statistics.getMean:\tno data => undefined result."
| otherwise = realToFrac numerator / fromIntegral denominator
where
(numerator, denominator) = Data.Foldable.foldr (\s -> (+ s) *** succ) (0, 0 :: Int) foldable
{- |
* Determines the /weighted mean/ of the specified numbers; .
* The specified value is only evaluated if the corresponding weight is non-zero.
* Should the caller define the result-type as 'Rational', then it will be free from rounding-errors.
-}
getWeightedMean :: (
Data.Foldable.Foldable foldable,
Fractional result,
Real value,
Real weight
)
=> foldable (value, weight) -- ^ Each pair consists of a value & the corresponding weight.
-> result
getWeightedMean foldable
| denominator == 0 = error "Factory.Math.Statistics.getWeightedMean:\tzero weight => undefined result."
| otherwise = numerator / realToFrac denominator
where
(numerator, denominator) = Data.Foldable.foldr (
\(value, weight) -> if weight == 0
then id --Avoid unnecessarily evaluation.
else (+ realToFrac value * realToFrac weight) *** (+ weight)
) (0, 0) foldable
{- |
* Measures the /dispersion/ of a /population/ of results from the /mean/ value; .
* Should the caller define the result-type as 'Rational', then it will be free from rounding-errors.
-}
getDispersionFromMean :: (
Data.Foldable.Foldable foldable,
Fractional result,
Functor foldable,
Real value
) => (Rational -> Rational) -> foldable value -> result
getDispersionFromMean weight foldable = getMean $ fmap (weight . (+ negate mean) . toRational) foldable where
mean :: Rational
mean = getMean foldable
{- |
* Determines the exact /variance/ of the specified numbers; .
* Should the caller define the result-type as 'Rational', then it will be free from rounding-errors.
-}
getVariance :: (
Data.Foldable.Foldable foldable,
Fractional variance,
Functor foldable,
Real value
) => foldable value -> variance
getVariance = getDispersionFromMean Math.Power.square
-- | Determines the /standard-deviation/ of the specified numbers; .
getStandardDeviation :: (
Data.Foldable.Foldable foldable,
Floating result,
Functor foldable,
Real value
) => foldable value -> result
getStandardDeviation = sqrt . getVariance
{- |
* Determines the /average absolute deviation/ of the specified numbers; .
* Should the caller define the result-type as 'Rational', then it will be free from rounding-errors.
-}
getAverageAbsoluteDeviation :: (
Data.Foldable.Foldable foldable,
Fractional result,
Functor foldable,
Real value
) => foldable value -> result
getAverageAbsoluteDeviation = getDispersionFromMean abs
-- | Determines the /coefficient-of-variance/ of the specified numbers; .
getCoefficientOfVariance :: (
Data.Foldable.Foldable foldable,
Eq result,
Floating result,
Functor foldable,
Real value
) => foldable value -> result
getCoefficientOfVariance l
| mean == 0 = error "Factory.Math.Statistics.getCoefficientOfVariance:\tundefined if mean is zero."
| otherwise = getStandardDeviation l / abs mean
where
mean = getMean l
-- | The number of unordered /combinations/ of /r/ objects taken from /n/; .
nCr :: (Math.Factorial.Algorithmic factorialAlgorithm, Integral i, Show i)
=> factorialAlgorithm
-> i -- ^ The total number of items from which to select.
-> i -- ^ The number of items in a sample.
-> i -- ^ The number of combinations.
nCr _ 0 _ = 1
nCr _ _ 0 = 1
nCr factorialAlgorithm n r
| n < 0 = error $ "Factory.Math.Statistics.nCr:\tinvalid n; " ++ show n
| r < 0 = error $ "Factory.Math.Statistics.nCr:\tinvalid r; " ++ show r
| n < r = 0
| otherwise = numerator `par` (denominator `pseq` numerator `div` denominator)
where
[smaller, bigger] = Data.List.sort [r, n - r]
numerator = Math.Implementations.Factorial.risingFactorial (succ bigger) (n - bigger)
denominator = Math.Factorial.factorial factorialAlgorithm smaller
-- | The number of /permutations/ of /r/ objects taken from /n/; .
nPr :: (Integral i, Show i)
=> i -- ^ The total number of items from which to select.
-> i -- ^ The number of items in a sample.
-> i -- ^ The number of permutations.
nPr 0 _ = 1
nPr _ 0 = 1
nPr n r
| n < 0 = error $ "Factory.Math.Statistics.nPr:\tinvalid n; " ++ show n
| r < 0 = error $ "Factory.Math.Statistics.nPr:\tinvalid r; " ++ show r
| n < r = 0
| otherwise = Math.Implementations.Factorial.fallingFactorial n r