Dmitry Malikov <malikov.d.y <at> gmail.com> writes: > > 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. _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe