The diagram shows the y argument to the fold on the left and the x argument to the fold on the right. So that cannot be the issue you are talking about.
The diagram shows y0 being used first, y1 second and so on, which matches what we saw happening in action. So that cannot be the issue you are talking about. But that leaves me confused (an all-too-common event) -- what is the behavior which you are talking about which does not conform to that diagram? Thanks, -- Raul On Tue, Sep 7, 2021 at 5:19 AM R.E. Boss <[email protected]> wrote: > > The main point I was trying to make was that F:. showed behaviour not conform > the diagram on https://code.jsoftware.com/wiki/Vocabulary/fcap. > The role of x and y seem to be interchanged. > However, then u F:.v~ should work, which does not. > > The advantage of fold is just that x can differ essentially from an item of > y, contrary to /\. , where all items are equal, and you are forced to use > boxes. > > > R.E.Boss > > > -----Original Message----- > From: Programming <[email protected]> On Behalf Of > Raul Miller > Sent: dinsdag 7 september 2021 10:16 > To: Programming forum <[email protected]> > Subject: Re: [Jprogramming] Fold experience > > Swapping the argument does not appear to influence the shape of the result. > > The results themselves are different, > > UV=:0,(,-@|.)=i.3 > foo=: {{ x+ y{UV }} > oof=: {{ y+ x{UV }} > > 0 0 0 (]F:.foo -: ]F:.foo~) 3 2 _3 > 0 > 0 0 0 (]F:.oof -: ]F:.oof~) 3 2 _3 > 0 > > That said, focusing on the variant which you described as providing the > desired behavior: > > 0 0 0 ]F:.oof 3 2 _3 > 0 0 1 > 0 1 1 > 0 1 0 > > This corresponds to: > 3 oof 0 0 0 > 0 0 1 > 2 oof 3 oof 0 0 0 > 0 1 1 > _3 oof 2 oof 3 oof 0 0 0 > 0 1 0 > > Which, in turn, somewhat matches the value selection mechanism of J's scan: > <\ 3 2 _3 > +-+---+------+ > |3|3 2|3 2 _3| > +-+---+------+ > > The difference between fold and scan being that fold reuses the result of the > previous evaluation while scan does not. > > I hope this makes sense, > > -- > Raul > > On Tue, Sep 7, 2021 at 2:09 AM R.E. Boss <[email protected]> wrote: > > > > [UV=:0,(,-@|.)=i.3 > > > > 0 0 0 > > > > 1 0 0 > > > > 0 1 0 > > > > 0 0 1 > > > > 0 0 _1 > > > > 0 _1 0 > > > > _1 0 0 > > > > > > foo=: {{ x+ y{UV }} NB. constructed conform the diagram on > > https://code.jsoftware.com/wiki/Vocabulary/fcap > > > > > > > > $0 0 0 (]F:. foo) 3 2 _3 > > > > 3 3 3 3 3 > > > > $0 0 0 (]F:. foo)~ 3 2 _3 > > > > 3 3 3 3 3 > > > > > > foo=: {{ y+ x{UV }} NB. y and x are swapped, counterintuitive > > > > > > > > $0 0 0 (]F:. foo) 3 2 _3 > > > > 3 3 > > > > 0 0 0 (]F:. foo) 3 2 _3 NB. this is the desired behaviour > > > > 0 0 1 > > > > 0 1 1 > > > > 0 1 0 > > > > $0 0 0 (]F:. foo)~ 3 2 _3 > > > > 3 3 > > > > Also remarkable is that swapping the arguments seems not to influence the > > result. > > Any clarification? > > > > > > R.E. Boss > > > > ---------------------------------------------------------------------- > > 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
