[Jprogramming] lines in display

[Roger Hui]

The binary representation 
http://www.jsoftware.com/help/dictionary/dx003.htm
provides lossless representation of J arrays
as a literal vector.  e.g.

   y=: o. i.2 3
   a=: 3!:1 y
   $a
72
   type <'a'
+----+
|noun|
+----+
   a 1!:2 <'\junk\xxx'
   y1=: 3!:2 (1!:1) <'\junk\xxx'
   y - y1  NB. i.e. bit-by-bit identical
0 0 0
0 0 0
   y -: y1
1
   y -:!.0 y1  NB. i.e. 0 tolerance,  bit-by-bit identical
1

3!:3 provides a related, more human-readable version of same.

   2 (3!:3) y
e200000000000000
0000000000000008
0000000000000006
0000000000000002
0000000000000002
0000000000000003
0000000000000000
400921fb54442d18
401921fb54442d18
4022d97c7f3321d2
402921fb54442d18
402f6a7a2955385e

There are also "components files" in the standard libraries.



----- Original Message -----
From: Ian Clark <earthspotty at googlemail.com>
Date: Tuesday, April 6, 2010 2:30
Subject: Re: [Jprogramming] lines in display
To: Programming forum <programming at jsoftware.com>

> I was afraid that would be the answer.
> 
> The inconvenience to my code is negligible. It just needs one more
> line, with an (if.) in it. What distresses me is my failure to
> understand why it happens. It makes me suspicious of my whole
> data-storage approach.
> 
> I need to store a 2-D integer array, call it z, in an ascii text file
> and recover it on reloading the file.
> Suppose 'a b'=:$z
> Proviso: z is one of several arrays of mixed data. I want to 
> retain a
> visual check on the file contents that they all match-up by rows
> (numbered: i.a). Without this proviso, a sensible thing to do is to
> store the contents of z as a vector and reconstruct it from a
> knowledge of the number of rows, (a).
> Taking a simple minded approach, however, I can use (":) to 
> stuff z in
> a file, and (".) to recover it again from the (2-D) file image. This
> seems adequate and reliable provided a>1 and b>1. I just 
> wouldn't have
> anticipated it breaking down for b=1, which is not an uncommon 
> case to
> arise.
> 
> Clearly this is not the approach an experienced J-er would take, and
> I'd like to know what that is.
> 
> I don't want to drag this thread off-topic. It just seemed 
> related in
> my mind to the problem of predicting the number of display-lines 
> in z
> -- or do I mean (":z)? Or (". ":z)?
> 
> Ian
> 
> 
> On Tue, Apr 6, 2010 at 12:29 AM, Roger Hui <rhui000 at shaw.ca> wrote:
> > It's a feature, an inevitable consequence of numeric
> > conversion and rank.  If it breaks your code you have
> > to rewrite your code.
> >
> >
> >
> > ----- Original Message -----
> > From: Ian Clark <earthspotty at googlemail.com>
> > Date: Monday, April 5, 2010 16:12
> > Subject: Re: [Jprogramming] lines in display
> > To: Programming forum <programming at jsoftware.com>
> >
> >> On not quite the same problem but a related one:
> >>
> >> If z is an integer table, under what conditions would you expect
> >> ": z
> >> to have the same number of rows as z? Under more restricted
> >> conditions, when is (z -: ". ": z) ?
> >>
> >> Clearly you can't expect rank to be preserved if z=: i.1 3 --since
> >> under ": the information gets lost to enable you to 
> distinguish it
> >> from i.3. But what about z=: i.3 1 ?
> >>
> >> Consider the following:
> >>
> >>    (". ": i.z) ; i.z=: 3 2
> >> +---+---+
> >> |0 1|0 1|
> >> |2 3|2 3|
> >> |4 5|4 5|
> >> +---+---+
> >>    (". ": i.z) ; i.z=: 3 1
> >> +-----+-+
> >> |0 1 2|0|
> >> |     |1|
> >> |     |2|
> >> +-----+-+
> >>
> >> Is this a bug or a feature? (It's breaking my code, for which 
> I have
> >> so far only found an inelegant fix).
> >>
> >> Ian
> >>
> >>
> >> On Fri, Apr 2, 2010 at 10:20 PM, Roger Hui 
> <rhui000 at shaw.ca> wrote:
> >> > If x is a rank 2 or higher numeric array, how many
> >> > lines are in the display of x?  For example,
> >> > there are 14 lines in the display of  i. 3 4 5 .
> >> >
> >> > I've worked on a related problem on-and-off for years,
> >> > starting in 1991, and only came to a good answer
> >> > for this problem just a few days ago.