c++ can be used to write UDFs for Excel.
It is the fastest way If you do not need dumped static data but you
prefer formula which will be recalculated every time when something
changes.

I use VBA to handle events only if I do not use VSTO.
All formulas I use are in C++.

This may be good for you, me and a few others.., but not the regular
Excel user since this requires a licensed version of Visual Studio.
Albeit we can assume Archidamos has said software, how does that
benefit the regular user who doesn't have the programming background.
Better to, perhaps, use Olaf's dhRichClient.dll and just set a ref to
the component you want to use. At least he provides this free (along
with samples/demos). In fact, I also have (from Olaf) a version of the
FilterMatches function I pointed the OP to that does the exact same
thing using the dhRichClient component. If I recall, it does the 2x
500000 comparisons and returns a 3rd list in less than 2 seconds (or
was that less than 1 second?).<g

--
Garry

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