Folks, I'm puzzled. Look here: <hansl> nulldata 6 set seed 123 series x = uniform() x[2] = NA series z = ok(x) && (x < 0.5) ? x : 0 print x z -o </hansl> this produces <output> x z 1 0.2103124 0.2103124 2 3 0.0003299 0.0003299 4 0.5931556 0.000 5 0.9869412 0.000 6 0.6499468 0.000 </output> Which is IMO wrong. I can see the logic in stipulating that anything involving NAs is NA but OTOH I would say that ( 0 && NA ) should be 0. Note, moreover, that <hansl> series z = missing(x) || (x >= 0.5) ? 0 : x </hansl> would work the way I'd expect it to. Am I missing something? ------------------------------------------------------- Riccardo (Jack) Lucchetti Dipartimento di Scienze Economiche e Sociali (DiSES) Università Politecnica delle Marche (formerly known as Università di Ancona) r.lucchetti(a)univpm.it http://www2.econ.univpm.it/servizi/hpp/lucchetti -------------------------------------------------------