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 <[email protected]> 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 <[email protected]>
> Date: Monday, April 5, 2010 16:12
> Subject: Re: [Jprogramming] lines in display
> To: Programming forum <[email protected]>
>
>> 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 <[email protected]> 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.
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