If any cell across many columns has a contradictory sign to any other

Apologies if this is a really simple problem that I can't see how to solve, but I've now been trying for some time and cannot.

I wish to check across several (18) colums whether any one of the cells has a number of the opposite sign to any other. A sort of "if any sign A1:R1 opposite sign to other, then Ignore, or Average the numbers". I know I can do it by an exhaustive set of ORs and ANDs checking each cell against each other (which is OK for a couple of columns), but gets too tedious as the number of columns rises.

OK; I'll try.

I wish to detect whether, in a range of 18 cells across 18 columns, any two cells have entries that are of opposite sign. If so, I want to ignore that whole row of data. If not, then just average the whole row of data.