The issue you discovered here is also discussed at http://www.jsoftware.com/help/jforc/empty_operands.htm
Properly speaking, it's an implementation issue rather than a dictionary issue (and, thus, subject to change, given sufficient motivation - but need a really good reason before making these kinds of changes, of course). Thanks, -- Raul On Wed, Dec 13, 2017 at 11:12 AM, Erling Hellenäs <[email protected]> wrote: > 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. >>>> >>> >> > > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
