The following array formula returns the number of unique values in a range named Data:

{=SUM(1/COUNTIF(Data,Data))}

The preceding formula is one of those “classic” Excel formulas that gets passed around the Internet. I don’t think anyone knows who originated it.

Useful as it is, this formula does have a serious limitation: If the range contains any blank cells it returns an error. The following array formula solves this problem:

{=SUM(IF(COUNTIF(Data,Data)=0,””,1/COUNTIF(Data,Data)))}

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