Thanks Raul, your solution is much nicer than mine.
-------------------------------------------- On Wed, 3/29/17, Raul Miller <[email protected]> wrote: Subject: Re: [Jprogramming] Unboxing after subarray function To: "Programming forum" <[email protected]> Date: Wednesday, March 29, 2017, 9:01 PM Here's a generalization which works on your first example (which happens to also be a better example): maxes=: [ # [ #"1 (2 2 $ [) >./@,;.3 ] T =: 10 10 $ 0 _2 12 100 2 4.5 1 7 _5.5 3.2 120 2 _100 3 5 18 4 2 maxes T 120 120 100 100 18 18 7 7 12 12 120 120 100 100 18 18 7 7 12 12 100 100 18 18 7 7 120 120 4.5 4.5 100 100 18 18 7 7 120 120 4.5 4.5 7 7 12 12 120 120 4.5 4.5 18 18 7 7 12 12 120 120 4.5 4.5 18 18 120 120 4.5 4.5 7 7 18 18 120 120 120 120 4.5 4.5 7 7 18 18 120 120 4.5 4.5 18 18 120 120 12 12 100 100 4.5 4.5 18 18 120 120 12 12 100 100 2 (]=maxes) T 0 0 0 1 0 0 0 1 0 0 1 0 0 0 0 1 0 0 0 1 1 0 0 0 1 0 0 1 0 0 0 0 1 0 0 0 0 0 0 1 0 1 0 0 1 0 0 0 0 1 0 0 0 1 0 0 1 0 0 0 0 1 0 0 0 0 1 0 0 0 0 0 0 1 0 1 0 0 1 0 0 0 0 1 0 0 0 1 1 0 1 0 0 0 0 1 0 0 0 0 Thanks, -- Raul On Wed, Mar 29, 2017 at 5:46 AM, Raul Miller <[email protected]> wrote: > maxes=: 3#3#"1 (2 2$3) >./@,;.3 ] > maxes T > 200 200 200 200 200 200 > 200 200 200 200 200 200 > 200 200 200 200 200 200 > 200 200 200 200 200 200 > 200 200 200 200 200 200 > 200 200 200 200 200 200 > (= maxes) T > 0 0 0 0 0 0 > 0 0 1 0 0 0 > 0 0 0 0 0 1 > 0 0 0 0 0 0 > 0 0 1 0 0 0 > 0 0 0 0 0 1 > > Like that? > > Thanks, > > -- > Raul > > > On Wed, Mar 29, 2017 at 5:38 AM, 'Jon Hough' via Programming > <[email protected]> wrote: >> Yes, the "stride" of each window is equal to its length, so in this case using ;.3 (with appropriate arguments) gives the same result as ;.1 . >> Regardless, my problem occurs after this part, I think. The problem is trying to unbox the boxed array, keeping the correct shape and element positions. >> If there is a way to do this without using ;. that would also be great. >> >> Just to reiterate, given an NxN array, T say, create a second NxN array, S say, such that the elements of S are either 1 or 0, depending on whether they are equal to the appropriate MxM subarray's max element, where M divides N. Sorry, that is a pretty ugly definition of the problem. >> >> Here's another example (using ;.3): >> >> ]T =: 6 6 $ 1 4 100 0 4 3 8 5 200 >> 1 4 100 0 4 3 >> 8 5 200 1 4 100 >> 0 4 3 8 5 200 >> 1 4 100 0 4 3 >> 8 5 200 1 4 100 >> 0 4 3 8 5 200 >> >> c =: ;.3 >> (2 2 $ 3 3 3 3) ((>./ = ])&.>@:<)c T NB. window has size 3x3 and stride 3x3, so creates 4 3x3 boxes >> >> >> ┌─────┬─────┐ >> │0 0 0│0 0 0│ >> │0 1 0│0 0 0│ >> │0 0 0│0 0 1│ >> ├─────┼─────┤ >> │0 0 0│0 0 0│ >> │0 1 0│0 0 0│ >> │0 0 0│0 0 1│ >> └─────┴─────┘ >> >> So, the problem is to get rid of the boxes, but keep the shape and positions of the array and its elements. >> >> -------------------------------------------- >> On Wed, 3/29/17, Rob Hodgkinson <[email protected]> wrote: >> >> Subject: Re: [Jprogramming] Unboxing after subarray function >> To: [email protected] >> Date: Wednesday, March 29, 2017, 6:19 PM >> >> Jon, I note Henry’s >> point about using <;.3 T if you wish to use the 2x2 >> tessellation windows as per Henry’s suggestion, that is >> fine. (it was my first approach on reading your question >> too). >> >> But I notice you are >> choosing to “slice” separate subarrays (non overlapping) >> so I gather your question is a neater way to reconstruct >> IsMax as a simple 10 10 array ? If so, you gave this: >> 10 10 $ , > |:"2 <"1 >> > IsMax >> >> Then my >> suggestion is this (which reproduces your final line >> only): >> >,"1&.>/ >> ,&.>/ IsMax >> >> HTH, >> Regards Rob >> >> >> > On 29 Mar 2017, at 6:54 pm, 'Jon >> Hough' via Programming <[email protected]> >> wrote: >> > >> > I should >> also mention that my verb(s) work for subarrays other than >> 2x2. >> > e.g. if T is a 12x12 array >> > T =: 12 12 $ 0 _2 12 100 2 4.5 1 7 _5.5 >> 3.2 120 2 _100 3 5 18 4 >> > is =: 12 $ 1 >> 0 0 >> > IsMax =: >> (is;is) ($$((>./=])@:,))&.>@:< >> interval T NB. max of 3x3 subarrays >> > >> 12 12 $ , > |:"2 <"1 > IsMax >> > >> > Also creates the >> correct array. >> > >> > >> -------------------------------------------- >> > On Wed, 3/29/17, 'Jon Hough' via >> Programming <[email protected]> >> wrote: >> > >> > Subject: >> [Jprogramming] Unboxing after subarray function >> > To: "Programming Forum" <[email protected]> >> > Date: Wednesday, March 29, 2017, 4:38 >> PM >> > >> > I have a NxN >> matrix. >> > For each 2x2 subarray of this >> (keep it simple, N is even), I >> > want to >> calculate the maximum value and if the value of that >> > cell equals the maximum of the 2x2 >> subarray write 1, else >> > write 0. >> > >> > e.g. >> > NB. T arbitrary 10x10 matrix >> > T =: 10 10 $ 0 _2 12 100 2 4.5 1 7 _5.5 >> 3.2 120 2 _100 3 5 >> > 18 4 >> > >> > interval =: ;.1 >> > is =: 10 $ 1 0 >> > >> > IsMax =: >> > >> (is;is) ($$((>./=])@:,))&.>@:< >> > interval T >> > >> > So IsMax shows which elements are the max >> values of the 4x4 >> > subarrays. >> > >> > Now I want to unbox >> and keep the indices correct. >> > >> > This appears to work >> > >> >> > 10 10 $ , > |:"2 <"1 >> > IsMax >> > >> > But is >> incredibly messy. I'm hoping there is a nicer/ more >> > terse / elegant way to do this. >> > >> > Thanks, >> > Jon >> > >> ---------------------------------------------------------------------- >> > For information about J forums see http://www.jsoftware.com/forums.htm >> > >> ---------------------------------------------------------------------- >> > For information about J forums see http://www.jsoftware.com/forums.htm >> >> ---------------------------------------------------------------------- >> For information about J forums see http://www.jsoftware.com/forums.htm >> ---------------------------------------------------------------------- >> For information about J forums see http://www.jsoftware.com/forums.htm ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
