Averages/Pythagorean means: Difference between revisions

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====Three applicatively defined functions====

These three functions (each combining the length of a list with some kind of fold over the elements of that same list), all share the same ~~general '''liftA2'''~~ structure.

These three functions (each combining the length of a list with some kind of fold over the elements of that same list), all share the same applicative structure.

<lang haskell>import ~~Control~~.~~Applicative~~ (~~liftA2~~)

<lang haskell>import Data.List (genericLength)

import Data.List (genericLength)

-- ARITHMETIC, GEOMETRIC AND HARMONIC MEANS ---------------

arithmetic, geometric, harmonic :: [Double] -> Double

arithmetic = ~~liftA2~~ (/) sum genericLength

arithmetic = (/) . sum <*> genericLength

geometric = ~~liftA2~~ (**) product ((1 /) . genericLength)

geometric = (**) . product <*> ((1 /) . genericLength)

harmonic = ~~liftA2~~ (/) genericLength (foldr ((+) . (1 /)) 0)

harmonic = (/) . genericLength <*> foldr ((+) . (1 /)) 0

-- TEST ---------------------------------------------------

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, mappend "\n A >= G >= H is " $ --

(show . and) $ zipWith (>=) xs (tail xs)

]

]</lang>

</lang>

<pre>("Arithmetic",5.5)("Geometric",4.528728688116765)("Harmonic",3.414171521474055)