Hi all !
It seems some related info did not make it into my blog and it is not
needed in my manual. My tweets about this are advertently cryptic:
-I found some interesting features of the real #J dyadic rank operator.
-Let's say the rank is zero and the argument is empty, how do you find
the resulting type and shape?
-Nothing can not be scalar, which can be executed to find the rank, can it?
-If you execute the verb on a scalar default object, what do you do if
you get an error? Which rank and type will you use?
More clearly:
I have found that J determines the type and shape of the result when
both arguments of the dyadic array operation helper program are empty by
executing the verb against default objects of both arguments. If the
result is an error, J hides this error. The result then gets another
rank than it should. The rank is then not consistent with the rank
obtained when the arguments are not empty.
This means that if you have a theory of how rank works, the theory will
be falsified by some of the results you get, which means your
understanding will most probably be fuzzy. You have to test all cases in
the terminal to verify that it indeed works when one or the other
argument, or both, are empty.
According to my notes, this is such a case:
$(i.0) (2 1$ =)"1 0 [i.0
0
$(i.1) (2 1$ =)"1 0 [i.1
1 2 1
Cheers,
Erling Hellenäs
Den 2017-12-13 kl. 16:24, skrev Erling Hellenäs:
This blogpost also contains related information.
https://erlhelinfotech.wordpress.com/2016/08/17/jwithatwist-scalar-operations/
/Erling
Den 2017-12-13 kl. 15:46, skrev Erling Hellenäs:
It seems you didn't read the parts of my manual I referenced. /Erling
Den 2017-12-13 kl. 14:39, skrev Raul Miller:
On Wed, Dec 13, 2017 at 3:46 AM, Erling Hellenäs
<[email protected]> wrote:
I doubt you can find reasonably accurate descriptions of this
functionality
(these four helper programs) anywhere else.
This suggests to me that you have not read
http://www.jsoftware.com/help/dictionary/dictb.htm
nor
http://www.jsoftware.com/help/dictionary/dicta.htm
I am surprised how many people have not read the reference manual -
not just in the J community but among technical people in general.
I really don't know what to make of this.
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