Can mapslices help here?
On Wednesday, March 23, 2016 at 6:59:59 PM UTC-5, Tomas Lycken wrote: > > Is there an effective pattern to iterate over the “endpoints” of an array > along a given dimension? > > What I eventually want to accomplish is to apply a function (in this case > an equality test) to the two end points along a particular dimension of an > array. I think the pattern is easiest explained by considering 1D, 2D and > 3D: > > # assume the existence of some scalar-valued function f(x,y) > > A1 = rand(10) > f(A1[1], A1[end]) # d == 1 (the only possible value) -> one evaluation > > A2 = rand(10, 15) > map(f, A2[1,:], A2[end,:]) # d == 1 -> 15 evaluations > map(f, A2[:,1], A2[:,end]) # d == 2 -> 10 evaluations > > A3 = rand(10, 15, 8) > map(f, A3[1,:,:], A3[end,:,:]) # d == 1 -> 15x8 evaluations > map(f, A3[:,1,:], A3[:,end,:]) # d == 2 -> 10x8 evaluations > map(f, A3[:,:,1], A3[:,:,end]) # d == 3 -> 10x15 evaluations > > I just want to consider one dimension at a time, so given A and d, and in > this specific use case I don’t need to collect the results, so a for-loop > without an allocated place for the answer instead of a map is just fine > (probably preferrable, but it’s easier to go in that direction than in the > other). What I’m struggling with, is how to generally formulate the > indexing expressions (like [<d-1 instances of :>, 1, <size(A,d)-d > instances of :>], but not in pseudo-code…). I assume this can be done > somehow using CartesianIndexes and/or CartesianRanges, but I can’t get my > mind around to how. Any help is much appreciated. > > // T > >
