Technically speaking, this is about insert rather than key. It's often the case that a F b and F/ a,:b give the same results.
(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
