How can I use the following SUMPRODUCT formula that counts only unique
records on filter list?

=SUMPRODUCT(($A$2:$A$20<"")/(COUNTIF($A$2:$A$20,$A$2:$A$20)+($A$2:$A$20="")))

The formula works fine on the list until I filter the data. I would like to
have the formula update based on the filtered data.

For example:

Unfiltered list:
Unfiltered result = 3
Data
1
1
1
2
2
3
3

Filtered list, which displays only 1 & 2:
Desired filtered result = 2
Data
1
1
1
2
2

Thanks,

Nick