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