Probably you meant
a table4 b
┌─┬───────┐
│ │0 1 2 3│
├─┼───────┤
│2│2 3 4 5│
│3│3 4 5 6│
│5│5 6 7 8│
└─┴───────┘
instead of using the standard table
a * table b
┌─┬─────────┐
│*│0 1 2 3│
├─┼─────────┤
│2│0 2 4 6│
│3│0 3 6 9│
│5│0 5 10 15│
└─┴─────────┘
Hallo Linda Alvord, je schreef op 21-11-11 14:03:
> 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
--
Met vriendelijke groet,
@@i=Arie Groeneveld
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