Google sheets formula to countunique rows with a condition

Question

I have a sheet where I keep track of some expenses. the data is formatted like this:

Vendor A | Plumbing | $250
Vendor B | Cleaning | 
Vendor A | Cleaning | $19
Vendor C | Washing  | $20
         |          |  
....

I want to count the number of unique vendors in the table where the 3rd column is greater than 0.

I tried =COUNTUNIQUE(C:C), but that counts the unique values of all the entries, even those where the value on column C is blank or 0.

Answer 1

You should filter the values before counting uniques:

=countunique(filter(A:A, C:C>0))