I don't quite have all the details worked out, but I am thinking in the following direction.
data=: 0 : 0 NB. notice this is different from June's data 0 p1 4 2 p1 6 3 p1 10 13 p1 15 0 p2 3 1 p2 5 7 p2 10 10 p2 11 14 p2 12 1 p3 9 5 p3 10 9 p3 20 7 p4 10 ) $dd =. ".@(-.&'p') ;._2 data Now I want to use scarce arrays $. on dd, but cannot figure out how exactly. I thought I would study the following example from the Vocabulary page, but I don't remember how to rewrite dd as a sparse array. ] d=: (?. 3 4$2) * ?. 3 4$100 0 0 0 0 85 0 0 0 0 59 33 0 ] s=: $. d 1 0 │ 85 2 1 │ 59 2 2 │ 33 In other words I don't know how to manually create an artificial version of the noun s above. I know it can be done. And if that is done with my noun dd, then it should be simple to create your result. -- (B=) ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
