Thanks Devon. Most helpful. I am a seasoned C/C++ programmer but a total newbie with J. I've surprised myself thus far by getting a working SDL2 and Postgres (libpq) wrapper up and running but they are more FFI code than idiomatic J.
I am having the same sorts of thoughts as I did when I first learned Lisp decades ago; how do you "do" anything! C has 'struct' but raw Lisp and car/cdr etc are more than enough in most cases provided the list order is well documented but I guess you can say that about anything. Thank you again, I guess the only way to find out is to actually cut some code. Next change I get I shall attempt my "rolling star field" effect within an SDL2 window., Sean. On Mon, 7 Dec 2020 at 17:01, Devon McCormick <[email protected]> wrote: > Hi - > As others have already indicated, J is most efficient with unboxed, simple > homogenous arrays. That said, it would be helpful to have an example of a > data structure, maybe one you have in C or C++, that you would like to > implement in J. > > Looking around, here is one of the more complex ones I found in C++ (from > https://codescracker.com/cpp/cpp-data-structures.htm): > > struct stud > { > int rollno; > char name[20]; > char branch[3]; > char batch[2]; > float marks[5]; > char grade; > }stud_var; > > This has two numeric and four character fields so may make us think we > should use a boxed array, maybe like this: > > students=. ,:101;'Joe Blow';'BAT';'FR';60 70 85 96.8 9;'B' > NB. Use ",:" to give us a one-row table > students=. students,202;'Cruella De Ville';'DOG';'SO';91 92 93 94 89;'A' > students=. students,303;'Christopher Xavier Columbus';'EXP';'JR';14 > 92 10 15 0;'F' > > We should specify the labels of each field: > labels=. 'rollno';'name';'branch';'batch';'marks';'grade' > > So we can use them like this: > > students{"1~labels i. <'name' > +--------+----------------+---------------------------+ > |Joe Blow|Cruella De Ville|Christopher Xavier Columbus| > +--------+----------------+---------------------------+ > > Alternatively, we could build this data structure using unboxed arrays > with distinct names in a namespace: > > rollno_students_=. 101 202 303 > name_students_=. >20{.&.>'Joe Blow';'Cruella De Ville';'Christopher > Xavier Columbus' > branch_students_=. 'BAT','DOG',:'EXP' > batch_students_=. 'FR','SO',:'JR' > marks_students_=. 60 70 85 96.8 9,91 92 93 94 89,:14 92 10 15 0 > grade_students_=. 'BAF' > > Notice how I now enforce the length limitations that the original C++ > example imposed, which is one of the things I dislike about these more > primitive languages: they force you to make data structure decisions > in advance of the actual data. > > name_students_ > Joe Blow > Cruella De Ville > Christopher Xavier C > > This length limitation does allow us to use simpler, unboxed, data > structures. Of course, we don't have to fix the maximum length in > advance in J: > > ]name_students_=. 'Joe Blow','Cruella De Ville',:'Christopher > Xavier Columbus' > Joe Blow > Cruella De Ville > Christopher Xavier Columbus > > It depends on how closely you wish to mimic the C++ or what trade-offs > you want to make. > > The unboxed arrays are often more efficient to process but the boxed > ones are more flexible, e.g.what if the number of "marks" varies > substantially from student to student? > > Also, boxed arrays can be quite efficient. As a rule of thumb, you > don't want to box very small things as each box incurs the overhead of > a pointer; for large things, say full names or paragraphs, the > overhead is amortized. > > I hope this helps, > > Devon > > > > > > > On Sun, Dec 6, 2020 at 9:40 PM Jimmy Gauvin <[email protected]> > wrote: > > > Hi, > > > > for some examples of J coding you can look at : : > > > > https://github.com/jitwit/aoc > > > > I found his site while playing at Advent of Code. > > > > > > Jimmy > > > > > > > > > > On Sun, Dec 6, 2020 at 7:44 PM bill lam <[email protected]> wrote: > > > > > you can use OOP class, object. They are implemented with locale. This > is > > > close enough to C structure. See labs. > > > > > > > > > > > > On Mon, Dec 7, 2020, 5:53 AM emacstheviking <[email protected]> wrote: > > > > > > > Rob and Raul.. > > > > > > > > Thanks chaps for the comments...the first thing I need to do is write > > > > -something- that does something and then go from there. > > > > It's not really a maths problem... well, in a way everything is > maths I > > > > guess but I am wanting to learn J and to write a game with it and > > that's > > > > pretty much it. > > > > > > > > I'll post some progress somewhere someday... > > > > > > > > Thanks again > > > > Sean > > > > > > > > > > > > On Sun, 6 Dec 2020 at 21:41, 'Rob Hodgkinson' via Programming < > > > > [email protected]> wrote: > > > > > > > > > Sean, the data structures in J work brilliantly for mathematical > > array > > > > > type problems. > > > > > > > > > > When the data framework you are seeking is more “structured” (akin > > to > > > > > Tables and Columns, or Keys and Values), then a more suited > structure > > > > might > > > > > require “jdb” for example (which makes use of boxing “tuples”). > > > > > This is a J compatible structured database for tables and columns. > > > > > > > > > > It really depends on the problem you are solving, for example for > > > Advent > > > > > of Code or other coding challenges they are usually mathematical in > > > > nature > > > > > and the J arrays are perfect, as they can be rectangular arrays > > > (matrices > > > > > etc) or nested arrays (boxed) so there is a lot of flexibility. > > > > > > > > > > With that in mind, I suggest learn the tools and then consider the > > > > > structure depending on the nature of the problem, but they are > pretty > > > > well > > > > > all there for you to use. > > > > > > > > > > HTH Rob > > > > > > > > > > > On 7 Dec 2020, at 7:50 am, emacstheviking <[email protected]> > > wrote: > > > > > > > > > > > > Hauke, > > > > > > Thanks for your comments. I have been scribbling notes on howto > go > > > > about > > > > > > it, my initial thoughts are that I need: > > > > > > > > > > > > genstar =: 3 : 0 > > > > > > generates an array of random numbers: initial x, initial y, > dy, > > > type > > > > > > > > > > > > updstar =: 3 : 0 > > > > > > in-place updates y by adding dy*timer interval > > > > > > if y is off screen then randomly reset this entry with y=0 > > > > > > > > > > > > Ha! This is going to be a lot of fun... > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > On Sun, 6 Dec 2020 at 20:36, Hauke Rehr <[email protected]> > > > > wrote: > > > > > > > > > > > >> If the atoms of x, y and dy are all numbers (or tuples > thereofª), > > > > > >> you can use a 3(or moreª)×(whatever common shape they have) > array. > > > > > >> Index into them along the correct axes, and you’ll get > > > > > >> back (or modify) a triplet (or triplets) (again, or moreª). > > > > > >> > > > > > >> And updating ought to be done in place as much as possible. > > > > > >> You don’t do updating most of the time, but when you need to, > > > > > >> do it in place if at all possible. > > > > > >> You’re guaranteed to work in place if you immediately assign > > > > > >> back to the name of the structure you amend, for example. > > > > > >> Also, take a look at the special combinations. > > > > > >> Personally, I avoid boxing as much as possible. > > > > > >> > > > > > >> Then again, that’s just my thoughts and I’m far from > > > > > >> as experienced as the average person on this list, I guess. > > > > > >> > > > > > >> Am 06.12.20 um 21:13 schrieb emacstheviking: > > > > > >>> What's the conventional wisdom / best practice on defining data > > > > > >> structures > > > > > >>> for an application? > > > > > >>> > > > > > >>> Given there is no explicit keyword/operator support like C > > (typdef, > > > > > >>> struct) is it merely a case of convention and using boxed > > > > structures. > > > > > I > > > > > >>> have read several operators that can modify structures both as > > new > > > > > >> aliased > > > > > >>> copies and in-place modifications but I do not have the > > experience > > > > > with J > > > > > >>> to know what's efficient at run time in time / memory etc. > > > > > >>> > > > > > >>> My specific use case is that of a vertically scrolling star > > > field... > > > > I > > > > > >>> intend to recreate and hopeful extend the tiny little game I > > wrote > > > > but > > > > > >>> never finished, screenshot here: > > > > > >>> http://seancharles.xyz/posts/2019-10-06-all-at-c.html > > > > > >>> > > > > > >>> In that I had a struct that had the x, y, dy and type values > but > > it > > > > > seems > > > > > >>> to me that given that J is all about arrays, it might be more > > > > efficient > > > > > >>> using parallel arrays i.e. x array, y array, dy array etc. > > > > > >>> > > > > > >>> Also, given that the state is being updated in a tight event > loop > > > > using > > > > > >> the > > > > > >>> time differential between frames to calculate the step motion > > (i.e. > > > > CPU > > > > > >>> speed independently), what are your thoughts on immutable > updates > > > > > >> producing > > > > > >>> new arrays or updating in place ? > > > > > >>> > > > > > >>> Thanks, > > > > > >>> Sean. > > > > > >>> > > > > > ---------------------------------------------------------------------- > > > > > >>> For information about J forums see > > > > http://www.jsoftware.com/forums.htm > > > > > >>> > > > > > >> > > > > > >> -- > > > > > >> ---------------------- > > > > > >> mail written using NEO > > > > > >> neo-layout.org > > > > > >> > > > > > >> > > > ---------------------------------------------------------------------- > > > > > >> 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 > > > > > -- > > Devon McCormick, CFA > > Quantitative Consultant > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm > ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
