[Haskell-cafe] How to use arrays efficiently?
lassoken at gmail.com
Fri May 16 04:19:29 EDT 2008
I have a list of index-value pairs and I want to get a list which is sorted
by the index and which contains index-wise sums of all the values.
Here is a function that does this (and a bit more).
pixelHistogram samples = let
index s t = let
x = round $ (fromIntegral imageWidth) * (1-s)
y = round $ (fromIntegral imageHeight) * (1-t)
in y*imageWidth + x
indexedSamples = [(index s t, color) | (s, t, color) <- samples]
pixelArray :: Array Int Color
pixelArray = accumArray (\+) black (0, imageWidth*imageHeight)
in elems pixelArray
The problem is that this function is very inefficient. It seems that the
whole indexedSamples list is stored in memory when creating pixelArray.
When I do some profiling I see that the heap consumption of this function
If I just write the samples list to a file instead of first summing them, I
get a nice and flat heap profile.
So how to do this efficiently?
-------------- next part --------------
An HTML attachment was scrubbed...
More information about the Haskell-Cafe