[Haskell-cafe] performance question

[Branimir Maksimovic]

Here is haskell version that is faster than python, almost as fast as c++.You need to install bytestring-lexing package for readDouble.
bmaxa at maxa:~/haskell$ time ./printMatrixDecay - < output.txtread 16384 matrix elements (128x128 = 16384)[0.00e0, 1.00e-8) = 0 (0.00%) 0[1.00e-8, 1.00e-7) = 0 (0.00%) 0[1.00e-7, 1.00e-6) = 0 (0.00%) 0[1.00e-6, 1.00e-5) = 0 (0.00%) 0[1.00e-5, 1.00e-4) = 1 (0.01%) 1[1.00e-4, 1.00e-3) = 17 (0.10%) 18[1.00e-3, 1.00e-2) = 155 (0.95%) 173[1.00e-2, 1.00e-1) = 1434 (8.75%) 1607[1.00e-1, 1.00e0) = 14777 (90.19%) 16384[1.00e0, 2.00e0) = 0 (0.00%) 16384
real    0m0.031suser    0m0.028ssys     0m0.000sbmaxa at maxa:~/haskell$ time ./printMatrixDecay.py - < output.txt(-) read 16384 matrix elements (128x128 = 16384)[0.00e+00, 1.00e-08) = 0 (0.00%) 0[1.00e-08, 1.00e-07) = 0 (0.00%) 0[1.00e-07, 1.00e-06) = 0 (0.00%) 0[1.00e-06, 1.00e-05) = 0 (0.00%) 0[1.00e-05, 1.00e-04) = 1 (0.00%) 1[1.00e-04, 1.00e-03) = 17 (0.00%) 18[1.00e-03, 1.00e-02) = 155 (0.00%) 173[1.00e-02, 1.00e-01) = 1434 (0.00%) 1607[1.00e-01, 1.00e+00) = 14777 (0.00%) 16384[1.00e+00, 2.00e+00) = 0 (0.00%) 16384
real    0m0.081suser    0m0.080ssys     0m0.000s
Program follows...
import System.Environmentimport Text.Printfimport Text.Regex.PCREimport Data.Maybeimport Data.Array.IOimport Data.Array.Unboxedimport qualified Data.ByteString.Char8 as Bimport Data.ByteString.Lex.Double (readDouble)
strataBounds :: UArray Int DoublestrataBounds = listArray (0,10) [ 0.0, 1.0e-8, 1.0e-7, 1.0e-6, 1.0e-5, 1.0e-4, 1.0e-3, 1.0e-2, 1.0e-1, 1.0, 2.0 ]
newStrataCounts :: IO(IOUArray Int Int)newStrataCounts = newArray (bounds strataBounds) 0
main = do    l <- B.getContents    let a = B.lines l    strataCounts <- newStrataCounts    n <- calculate strataCounts a 0    let        printStrataCounts :: IO ()        printStrataCounts = do            let s = round $ sqrt (fromIntegral n::Double) :: Int            printf "read %d matrix elements (%dx%d = %d)\n" n s s n            printStrataCounts' 0 0        printStrataCounts' :: Int -> Int -> IO ()        printStrataCounts' i total             | i < (snd $ bounds strataBounds) = do                count <- readArray strataCounts i                let                     p :: Double                    p = (100.0*(fromIntegral count) :: Double)/(fromIntegral n :: Double)                printf "[%1.2e, %1.2e) = %i (%1.2f%%) %i\n" (strataBounds ! i) (strataBounds ! (i+1))                                                                 count p (total + count)                printStrataCounts' (i+1) (total+count)            | otherwise = return ()    printStrataCounts
calculate :: IOUArray Int Int -> [B.ByteString] -> Int -> IO Intcalculate _ [] n = return ncalculate counts (l:ls) n = do    let         a = case getAllTextSubmatches $ l =~ B.pack "matrix.*= ([0-9eE.+-]+)$" :: [B.ByteString] of                [_,v] -> Just (readDouble v) :: Maybe (Maybe (Double,B.ByteString))                _ -> Nothing        b = (fst.fromJust.fromJust) a        loop :: Int -> IO()        loop i            | i < (snd $ bounds strataBounds) =                 if (b >= (strataBounds ! i)) && (b < (strataBounds ! (i+1)))                then do                    c <- readArray counts i                    writeArray counts i (c+1)                else                     loop (i+1)            | otherwise = return ()    if isNothing a        then             calculate counts ls n        else do            loop 0            calculate counts ls (n+1)

From: nicolasbock at gmail.com
Date: Fri, 8 Feb 2013 12:26:09 -0700
To: haskell-cafe at haskell.org
Subject: [Haskell-cafe] performance question

Hi list,
I wrote a script that reads matrix elements from standard input, parses the input using a regular expression, and then bins the matrix elements by magnitude. I wrote the same script in python (just to be sure :) ) and find that the python version vastly outperforms the Haskell script.


To be concrete:
$ time ./createMatrixDump.py -N 128 | ./printMatrixDecayreal    0m2.655s
user    0m2.677ssys     0m0.095s


$ time ./createMatrixDump.py -N 128 | ./printMatrixDecay.py -
real    0m0.445suser    0m0.615ssys     0m0.032s
The Haskell script was compiled with "ghc --make printMatrixDecay.hs".


Could you have a look at the script and give me some pointers as to where I could improve it, both in terms of performance and also generally, as I am very new to Haskell.


Thanks already,
nick


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