On Fri, Nov 18, 2011 at 4:15 PM, Raul Miller <[email protected]> wrote: > Technically speaking, this is about insert rather than key.
Yep, true. > It's often the case that a F b and F/ a,:b give the same results. I just found the f//./ usage a little opaque when I first came across it (probably just because it was a little difficult to visually parse) and thought it might be nice to see the identity discussed in the examples section on this wiki page. Best, M > (There are some cases where the result would be different for a generic F > but which are the same for a specific F, but these are cases where the > specific F that gives the same results is ignoring the difference in the > arguments.) > > -- > Raul > > On Fri, Nov 18, 2011 at 6:10 AM, Marc Simpson <[email protected]> wrote: > >> Hi all, >> >> Reading through Roger's essay on the key adverb >> (http://www.jsoftware.com/jwiki/Essays/Key), I thought it might be >> useful to add a demonstration of the f//./ usage (found, for example >> in Eugene McDonnell's discussion in "At Work and Play in the Fields of >> J", http://www.jsoftware.com/papers/eem/AWPFJ/10.htm)? >> >> Recreating the data in the current example, >> >> y =. 6 5 9 2 4 9 0 7 0 4 6 8 3 8 1 2 8 0 0 2 >> a =. 4.6 5.5 7.9 5.2 5.4 3.9 6 5.7 6 9.4 4.6 7.8 1.3 1.8 5.1 9.2 7.8 6 9 >> 6.2 >> >> the following equivalences could be demonstrated, >> >> (~.y) ,: y +//. a >> 6 5 9 2 4 0 7 8 3 1 >> 9.2 5.5 11.8 20.6 14.8 27 5.7 17.4 1.3 5.1 >> (~.y) ,: +//./ y,:a >> 6 5 9 2 4 0 7 8 3 1 >> 9.2 5.5 11.8 20.6 14.8 27 5.7 17.4 1.3 5.1 >> >> and perhaps broken down a little (without the nub of y lamination) to >> show what's going on more clearly: >> >> y +//. a >> 9.2 5.5 11.8 20.6 14.8 27 5.7 17.4 1.3 5.1 >> +//./ y,:a >> 9.2 5.5 11.8 20.6 14.8 27 5.7 17.4 1.3 5.1 >> >> It might also be worth pointing out that f//./ is handy when you have >> a matrix rather than two vectors. >> >> Best, >> M >> ---------------------------------------------------------------------- >> 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
