在下面的代码中，我基准测试了Bucket Sort的实现。bucketsort函数使用_bucketsort的结果，但将其展平为单个列表。令我惊讶的是，此过程(Map.toList)需要很多时间。
module Main where
import System.Random
import Criterion.Main
import qualified Data.List as List
import qualified Data.Map as Map
import Data.Maybe
insert :: (Ord a) => a -> [a] -> [a]
insert x [] = [x]
insert x (y:xs)
| x <= y = x:y:xs
| otherwise = y : insert x xs
bucketsort :: (Integral a) => [a] -> [a]
bucketsort xs = List.concatMap (snd) . Map.toList $ _bucketsort xs Map.empty
_bucketsort :: (Integral k) => [k] -> Map.Map k [k] -> Map.Map k [k]
_bucketsort [] map = map
_bucketsort (x:xs) map =
let bucket = x `div` 3
bucketlist = maybeToList $ Map.lookup bucket map
bucketInsert x [] = [x]
bucketInsert x xs = insert x $ head xs
ys = bucketInsert x bucketlist
newMap = Map.insert bucket ys map
in _bucketsort xs newMap
dataset n = List.take n $ randomRs (0, 9999) (mkStdGen 42)
main = defaultMain [ bench "bucketsort 96080" $ whnf bucketsort ((dataset 96080) :: [Int])
, bench "_bucketsort 96080" $ whnf _bucketsort ((dataset 96080):: [Int])]
这是Criterion进行基准测试的结果:
C:\>benchmark_bucketsort.exe
warming up
estimating clock resolution...
mean is 1.353299 us (640001 iterations)
found 1278266 outliers among 639999 samples (199.7%)
638267 (99.7%) low severe
639999 (100.0%) high severe
estimating cost of a clock call...
mean is 105.8728 ns (8 iterations)
found 14 outliers among 8 samples (175.0%)
7 (87.5%) low severe
7 (87.5%) high severe
benchmarking bucketsort 96080
collecting 100 samples, 1 iterations each, in estimated 24.35308 s
Warning: Couldn't open /dev/urandom
Warning: using system clock for seed instead (quality will be lower)
mean: 187.2037 ms, lb 182.7181 ms, ub 191.3842 ms, ci 0.950
std dev: 22.15054 ms, lb 19.47241 ms, ub 25.64983 ms, ci 0.950
variance introduced by outliers: 84.194%
variance is severely inflated by outliers
benchmarking _bucketsort 96080
mean: 8.823789 ns, lb 8.654692 ns, ub 9.049314 ns, ci 0.950
std dev: 952.9240 ps, lb 723.0241 ps, ub 1.154097 ns, ci 0.950
found 13 outliers among 100 samples (13.0%)
13 (13.0%) high severe
variance introduced by outliers: 82.077%
variance is severely inflated by outliers
如果我的
bucketsort函数可以写得更好并且希望更快，我也不会感到惊讶。但是到目前为止，我还没有弄清楚如何做。另外，我对Haskell代码的任何改进/评论都非常受欢迎。
最佳答案
您没有在第二个基准测试中完全应用_bucketsort，因此仅对WHNF评估了部分应用的函数，这无疑很快。
将相关行更改为
main = defaultMain [ bench "bucketsort 96080" $ whnf bucketsort ((dataset 96080) :: [Int])
, bench "_bucketsort 96080" $ whnf (flip _bucketsort Map.empty) ((dataset 96080):: [Int])]
产量(在我的机器上):
warming up
estimating clock resolution...
mean is 2.357120 us (320001 iterations)
found 2630 outliers among 319999 samples (0.8%)
2427 (0.8%) high severe
estimating cost of a clock call...
mean is 666.7750 ns (14 iterations)
found 1 outliers among 14 samples (7.1%)
1 (7.1%) high severe
benchmarking bucketsort 96080
collecting 100 samples, 1 iterations each, in estimated 34.66980 s
mean: 244.3280 ms, lb 238.0601 ms, ub 250.6725 ms, ci 0.950
std dev: 32.37658 ms, lb 28.02356 ms, ub 38.10187 ms, ci 0.950
found 3 outliers among 100 samples (3.0%)
3 (3.0%) low mild
variance introduced by outliers: 87.311%
variance is severely inflated by outliers
benchmarking _bucketsort 96080
collecting 100 samples, 1 iterations each, in estimated 24.65911 s
mean: 244.9425 ms, lb 239.1011 ms, ub 251.0300 ms, ci 0.950
std dev: 30.68877 ms, lb 26.48151 ms, ub 36.20961 ms, ci 0.950
variance introduced by outliers: 86.247%
variance is severely inflated by outliers
此外请注意，此基准测试并未完全强制使用列表，因为列表上的
whnf仅会评估顶级构造函数。这解释了为什么两个基准现在都具有几乎相同的性能。将两个基准都切换为nf会将时间分别更改为369.3022ms和354.3513ms，这使得bucketsort再次变慢了一点。