note sundialsvc4 <p> In the &ldquo;further food for thought&rdquo; department, it occurs to me that this is not entirely a pure-combinatorics problem. &nbsp; One filter might appear to be &ldquo;better&rdquo; in one situation than it would have been in another, <i>i.e.</i> because another filter did precede it, and that filter did remove elements perhaps more-efficiently than it would have done. &nbsp; A key factor of consideration might be ... and only you could have the answer to this ... is the most important goal that the result-set be reduced to its minimum practicable size, or that the filter-set should reduce the result-set as far as it can manage to do within a strictly limited amount of CPU time? &nbsp; How predictable and consistent are these &ldquo;costs,&rdquo; and upon what do they depend? </p><p> If you can by any means see your way to making this a true optimization problem then by all means do that ... but I guess that you can&rsquo;t because, if you could, you probably would not have a choice of more-than-one filter. &nbsp; It is quite an interesting sort of problem and my guess is that the solution of choice will be a heuristic rather than an algorithm much less a proof. &nbsp; You&rsquo;ll come up with a self-adapting method that produces good-enough results and that does so consistently, perhaps never knowing whether a few milliseconds more could have been shaved at any particular instant. </p> 1011650 1011650