Dmitry Malikov
Playing around with repa arrays and got some questions.
1) How I can get list of indexes of array that suffice some predicate?
> a1 AUnboxed (Z :. 3) (fromList [False,False,True]) it :: Array U (Z :. Int) Bool
Indexes of element that satisfying specific predicate could be obtained like that:
> (\a p → Data.List.map (subtract 1 . snd) $ filter (p . fst) $ zip (toList a) [1..]) a1 (== False) [0,1]
Looks ugly. How REPA users used to do filtering like that without converting to list?
I hope someone will correct me if I am wrong and furthermore I was not entirely clear what you were trying to do but it seems to me that if you want to filter out an unknown number of elements from a collection then repa is the wrong abstraction to use. You can however filter out a known number of elements e.g. xs = Repa.fromListUnboxed (Z :. 3) [1, 2, 3] removeOne ix xs = Repa.fromFunction (Z :. dx - 1) (\(Z :. jx) -> xs ! (Z :. f jx)) where Z :. dx = Repa.extent xs f jx | jx < ix = jx | otherwise = jx + 1 test = Repa.computeP $ removeOne 1 xs :: IO (Array U DIM1 Float) Does that help? Dominic.