Roger Thank you very much for this suggestion. Building a literal matrix like this and using the key adverb is a very practical suggestion.
Furthermore, by using i.#V as the right argument to the function derived from /. then as well as calculating the group totals, several other statistics can be computed at the same time and at minimal extra cost. Regards David > Roger Hui rhui000 at shaw.ca > Tue Jul 5 00:38:57 HKT 2011 > > As you said, for 10 sparse axes in J64 each datum > requires 80 bytes for the indices. If you encode the > indices as columns in a literal matrix, then the indices > for each datum requires 10 bytes. The computations > would be even simpler if you also encode each of > the "high cardinality dimensions" (400) as 2 columns > in this literal matrix. > > That is, you'd have a literal matrix I with 16=+/ 10 3#1 2 > columns, and a corresponding vector v of the numeric > values. (Each a mapped file?) Both selection and > summation are not too complicated, with the latter > depending heavily on the key adverb (/.). The complications > are not too bad compared to the alternatives. > ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
