Excel count unique values if second criteria is also satisfied

I currently have a formula to count all unique values of a range, however I would like to expand this count all unique values, if a second column meets a second requirement, for example.

      A        B
1  Name     Location
2  Tim      Onsite
3  Tim      Onsite
4  Ben      Offsite
5  Lisa     Onsite

In this instance the unique values of Name will return 3, for that I am using

=SUMPRODUCT(1/COUNTIF(A2:A5,A2:A5&""))

However when I try to use a COUNTIFS it always returns an error.

=SUMPRODUCT(1/COUNTIFS(A2:A5,A2:A5&"", B2:B5, "Onsite"))

Any ideas how to achieve this, so from my sample data, counting Onsite would return 2, (3 unique values, 2 of them satisfying the onsite criteria)

Answer

You need a bit more conversion:

=SUM(IFERROR(1/COUNTIFS(A2:A5,A2:A5&"", B2:B5, "Onsite"),0))

This is an array formula, so after inserting you need to press CTRL + SHIFT + ENTER