histogram

gistfile1.hs

import Data.List (sort)

-- make histogram
--
-- @param xs [Double] Data array
-- @param delta Double histogram's step width.
-- @param pivot Double 
--
histogram :: Double -> Double -> [Double] -> [(Double,Int)]
--  sortすると遅くなりそうだけど、再代入できないからこんな感じなのかな
--  最初にrangeごとにカウンターを用意して、数えていくほうが計算量が少なそう
histogram delta _ _ 
    | 0 >= delta = error "delta must be >0."
histogram delta pivot xs = (reverse (make' pivot (-delta) (reverse a))) ++ (make' pivot delta b)
    where
    (a, b) = break (> pivot) $ sort xs
    make' _ _ [] = []
    make' d inc xs = (d, length a) : make' (d + inc) inc b
        where
        comp
            | 0 > inc     = (>)
            | otherwise = (<)
        (a, b) = break (comp d) xs