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
