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
