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
