Counting unique instances in an array.

Can someone help me with this?

I want to use a formula that will look at an array of cells and tell me how many unique values there are.

For example, in the array below, the answer would be 4.

A
A
A
B
B
C
C
C
C
D
D

Is there an easy formula for this?

Try this formula where your data is in A1:A10

=SUMPRODUCT((A1:A10<>"")/COUNTIF(A1:A10,A1:A10&""))

=SUMPRODUCT((A1:A6<>"")/(COUNTIF(A1:A6,A1:A6&"")))
assuming cells are text and you make the range equal yours