source data with thousands of records.

Depending on how many records this could be slow to calculate.

Assuming your data is in the range A2:B11 with no empty/blank cells...

D2:Dn = Product 1, Product 2, etc.

Enter this array formula** in E2 and copty down as needed:

=SUM(IF(FREQUENCY(IF(B$2:B$11=D2,MATCH(A$2:A$11,A$ 2:A$11,0)),ROW(A$2:A$11)-ROW(A$2)+1),1))

** array formulas need to be entered using the key combination of
CTRL,SHIFT,ENTER (not just ENTER). Hold down both the CTRL key and the SHIFT
key then hit ENTER.

--
Biff
Microsoft Excel MVP


"Chin Huat" wrote in message
...
This is an extract of my source data with thousands of records. I want
to know the no. of cutomers (unique count) associated with each
product without deleting any records from the source file. Is there
any formula/function which I can use? E.g For product 2, there are 4
unique customers while product 4 has only 1 unique customers?

Customer 1 Product 1
Customer 2 Product 2
Customer 7 Product 2
Customer 5 Product 2
Customer 3 Product 2
Customer 2 Product 2
Customer 2 Product 3
Customer 3 Product 4
Customer 4 Product 4
Customer 4 Product 4