I am trying to determine the number of individual people used on a project.

I have 3 Columns of Data - e.g.

Project ID 1 Project ID 2 Person Name
Project A Project 123 Joe Bloggs
Project A Project 456 Joe Bloggs
Project A Project 456 Mary Little-Lamb
Project B Project 123 Jim Smith
Project B Project 123 Mary Little-Lamb

The forumla I need will determine the number of unique people against the
unique projects in both columns. So the end result will look like this:

Project ID 1 Project ID 2 No. People
Project A Project 123 1
Project A Project 456 2
Project B Project 123 2

I've been trying to use the (SUM(IF(FREQUENCY.... to determine the number of
unique names against the project ID, but I'm having trouble with getting the
formula to lookup the applicable reference and then return the value, all I
get is the entire number of unique values regardless of which Project they
are against.

I appreciate any help you can give.

Thanks