On 09.02.2013 01:02, Nicolas Bock wrote:
Yes, a histogram. The binning code is really a little awkward. I haven't
gotten used to thinking in terms of inmutable objects yet and this list
appending is really a pretty bad hack to kind of allow me to increment
the bin counts. How would one do this more haskellishish?
Histogramming is a bit awkward in haskell. If we want to stick to
immutable data types best choice is to have map bin → number of entries.
For every new entry select bin and add 1 to its content.
But if we want to store data in array we have to deal with mutable
state. It's not realistic to copy array on every update. For that case I
wrote I library histogram-fill[1]. Below is program which does
approximately same thing.
> import Data.Histogram.Fill
> import Data.Histogram (Histogram)
>
> hb :: HBuilder String (Histogram LogBinD Int)
> hb = forceInt -<< mkSimple (logBinDN 1e-8 10 10) <<- read
>
> main :: IO ()
> main = do
> l <- getContents
> print $ fillBuilder hb $ lines l
I cheated and used sed to strip unused data. It uses String so it's
still slower than python.
$ time (python gen.py -N 300 | sed 's/.*=//' | ./printMatrixDecay )
real 0m0.958s
user 0m2.096s
sys 0m0.052s
$ time (python gen.py -N 300 | python printMatrixDecay.py -)
real 0m0.590s
user 0m0.952s
sys 0m0.016s
[1] http://hackage.haskell.org/package/histogram-fill
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