(Simple) Unique Count - Formula problem

Hi,

I'm having some difficulties creating a unique count formula. I am trying to look-up a supplier name against a data extract, and count the number of Categories they fall under.

For example, the 2 fields I'm concerned with on the look-up table are:

A B
Supplier | Category

A1| Extreme Sport | Event Services
A2| Extreme Sport | Media Production
A3| Extreme Sport | Media Production
A4| One Media | Media Production


IE. Extreme Sport would fall under 2 categories (Event Services & Media Production). On my report I need it to look like this:


A B
Supplier | Number of Categories

A1| Extreme Sport | 2
A2| One Media | 1


However, I can't seem to find a way to use a COUNTIF that doesn't return the number lines, rather than the number of unique values. I was thinking about a INDEX/MATCH but imagine it will have the same problem.

Any help would be greatly appreciated!

Cheers
Alan