table4 not table a=:2 3 5 b=:0 1 2 3 table4 =: 2 2 $ '';];([:,.[);+/ a table4 b ┌─┬───────┐ │ │0 1 2 3│ ├─┼───────┤ │2│2 3 4 5│ │3│3 4 5 6│ │5│5 6 7 8│ └─┴───────┘
2011/11/21 Linda Alvord <[email protected]> > My role was to create simple problems that students could understand fully, > so they would be ready for the graduate courses you describe. All the > issues > like rank are useless when they do not yet have an appreciation for the > elegance of a vector. > > Your comments could form the basis for an excellent syllabus for a course > in > J at the college level! In addition, they should raise questions the you > programmers on this forum will need to understand as they are ready. > > Maybe there are changes in j701 that are causing this not to work. > I'll leave this one for the real computer wizards. > > > table4 =: 2 2 $ '';];([:,.[);+/ > a=:2 3 5 > b=:0 1 2 3 > a table b > |domain error > | (((#~LF-.@e.])5!:5<'u');,.y),.({.;}.)":x,y u/x > > > > -----Original Message----- > From: [email protected] > [mailto:[email protected]] On Behalf Of Fraser Jackson > Sent: Sunday, November 20, 2011 3:19 PM > To: Programming forum > Subject: Re: [Jprogramming] table challenge in simple J > > In this thread there has been a focus on the visual appearance > of the output. But many of the functions fail what I consider > a basic requirement in many programming situations. > > We can get visual identity, but the displayed objects may > be of different shape or type. > > If the objective is purely to produce a pretty display then > conversion to literal may be fine. If it is to create > a result which is to be used in further calculations it may not. > > After my post Dan Lettow suggested off line that I should > incorporate ": in future solutions. I looked at it, drafted > a simple addendum to my post but did not post it. > > Now that we have some more solutions it is clear that Linda's > problem specification is not really adequate in a J environment. > > (1) We need to specify the ranks of the function, or some > very powerful defaults will be applied. > > If we want the full power of insert then the default is _ _ _ . > I think there are strong grounds for wanting to preserve that. > > To handle what Kip called extreme cases, it was suggested > that the arguments should be converted to vectors. That is > fine for functions defined over a pair of numeric scalars. > > We might want to generalise that in many different ways. > Suppose we had two tables of points with three coordinates, > and wish to tabulate some function dependent on them - > perhaps the distance between them. > > The function in table need not be of rank 0 0 though that > is the commonest form used for illustration. > > Linda's problem was interpreted by most contributors as > writing a function for rank 1 arguments on left and right > and the table function as having rank 0. > > > (2)If we are to preserve fidelity then we need to > consider the type of the result. Again several contributors > have proposed solutions in which some of the boxed displays > are literal. That gives a pretty display, but it is not > true to the original argument. A sum of a numeric and > a literal vector does not make sense. > > One thing we often find in J is that a structure which is > based on the algorithmic needs is different from the > best way of presenting the information. > > There is a need for a table function which preserves > all features of the J objects, but also a need for a > listtable function which displays the results using forms > which assist visual interpretation. > > They are different needs and we should recognize them. In > statistical programs having both table and listtable which > operates on the result a table call is a common way of > dealing with this. > > (3) Sometimes it is easier to build up a set of results > of interest and then assemble them. Someone may have > suggested it, but if they have I did not notice it. > > table4 adopts that approach. > > table4 =: 2 2 $ '';];([:,.[);+/ > > > It works when the left argument is of rank 0 or 1 but it is not > totally satisfactory visually and does not work at all > well otherwise. > > > > Linda raised a very simple problem. Her intuition that it > would raise interesting and important issues has indeed > been true. > ----- Original Message ----- > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm > > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm > -- Björn Helgason, Verkfræðingur Fornustekkum II 781 Hornafirði, t-póst: [email protected] gsm: +3546985532 twitter: @flugfiskur http://groups.google.com/group/J-Programming Tæknikunnátta höndlar hið flókna, sköpunargáfa er meistari einfaldleikans góður kennari getur stigið á tær án þess að glansinn fari af skónum /|_ .-----------------------------------. ,' .\ / | Með léttri lund verður | ,--' _,' | Dagurinn í dag | / / | Enn betri en gærdagurinn | ( -. | `-----------------------------------' | ) | (\_ _/) (`-. '--.) (='.'=) ♖♘♗♕♔♙ `. )----' (")_(") ☃☠ ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
