If you are entering data in one row across several columns and you want
to prevent duplicates from being entered in that one row (Assume Row 2
for this example):

Select the row, then click on DataValidation and select "Custom" in
the dropdown list in the "Settings" tab. Then enter this formula in
the "Formula" window: =COUNTIF(2:2,A$2)<=1 .

Now an error message pops up whenever the user attempts to enter the
same data twice in Row 2.

If you want to prevent duplicates in a column (Assume Col A) instead
of a row then the formula to enter is: =COUNTIF(A:A,$A1)<=1 .


--
neopolitan


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