unless the arrays are sorted, I would think you would have to loop and
compare on each element.

If they were on a worksheet, you could use the countif formula.

--
Regards,
Tom Ogilvy

"Marston" wrote in message
om...
I have two relatively large 1D arrays (I could make them into a two D
with a dummy column if that would help, but I can't imagine how). Both
arrays contain a series of strings, with each string being exactly the
same length (in this case 18 characters). The characters are numbers
as strings. Each array contains 20,000-30,000 elements.

The challenge is finding a fast way to compare each element in one
array to see if it exists in the second array. I find that if I do
this through any simple stepwise looping it takes forever. Any
suggestions?