Of course. (A place where J and APL differ.) Thanks Jan-Pieter. Mike
> On Apr 16, 2020, at 12:00, Jan-Pieter Jacobs <[email protected]> > wrote: > > Actually, the dimension lost is the first, as insert [0] (u/) inserts u > between the items [1]. > > Demonstration: > > $ foo =: i. 2 3 4 > 2 3 4 > $ +/ foo > 3 4 > > [0]: https://code.jsoftware.com/wiki/Vocabulary/slash > [1]: https://code.jsoftware.com/wiki/Vocabulary/AET#Item > > Cheers, > > Jan-Pieter > > Op wo 15 apr. 2020 om 20:54 schreef Mike Powell <[email protected]>: > >> Thomas, >> >> I J there is not really anything for a column vector. If an object, like >> your rvec, has a single dimension it’s a vector. If it has two dimensions, >> as does cvec, it’s a matrix. That’s different from most conventional >> mathematical notation. >> >> When you do the summation with +/ you lose a dimension in the result. So a >> vector sums to a scalar and a matrix (with any number of columns) sums to a >> vector. The dimension lost is the last. >> >> It’s a simple rule that’s consistently applied. So the summation of a rank >> 5 array is a rank 4 array. (Of course, the sum of a scalar is still just a >> scalar.) And the same rule applies if the function is multiply rather than >> add for example. >> >> One of the joys of writing in J (or APL or K) is that very often the code >> you write works for arrays of any rank. >> >> Mike >> >>> On Apr 15, 2020, at 10:33 AM, Thomas Bulka <[email protected]> >> wrote: >>> >>> Hello everyone, >>> >>> I do have some difficulties in understanding a certain behavior. Let's >> assume, I define the classical mean verb, a row vector and a column vector: >>> >>> mean =: +/ % # >>> rvec =: 1 2 3 >>> cvec =: 3 1 $ 1 2 3 >>> >>> When I apply mean to rvec I get the result 2 (as expected), which >> happens to be a scalar ($$ mean rvec yields 0). When I apply mean to cvec >> the result is a vector ($$ mean cvec yields 1). I'd like to understand, why >> this behavior has been chosen. Do you have any hints for me? >>> >>> Regards, >>> >>> Thomas >>> >>> ---------------------------------------------------------------------- >>> For information about J forums see http://www.jsoftware.com/forums.htm >> >> ---------------------------------------------------------------------- >> For information about J forums see http://www.jsoftware.com/forums.htm >> > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
