Countif Unique Records in List Match Criteria

I'm trying to figure out a formula for this one. From reading other posts I know I'll need a combination of the Countif formula, Frequency formula, Match formula, and Row formula. I'm just not sure how to put them together.

Example: I'm trying to write a formula that will tell me how many days (therefore unique records) each individual worked. Let's focus just on Aaron. The result for Aaron should return the value of 4, because there were only 4 unique records tied to his name. Therefore Charlie = 1 day, and Doug = 3 days. How can I write this formula for Aaron? (I can figure out the rest if I can get the first one started).

Thanks!

	A	B
1	Associate	Date
2	Aaron	6/16/12
3	Aaron	6/16/12
4	Aaron	6/16/12
5	Aaron	6/17/12
6	Aaron	6/17/12
7	Aaron	6/18/12
8	Aaron	6/19/12
9	Charlie	6/12/12
10	Charlie	6/12/12
11	Charlie	6/12/12
12	Doug	6/27/12
13	Doug	6/28/12
14	Doug	6/28/12
15	Doug	6/29/12

Array confirmed with Shift Ctrl Enter

=SUM(IFERROR(1/COUNTIFS($A$2:$A$15,"Aaron",$B$2:$B$15,$B$2:$B$15),0))

"Aaron" could be entered in another cell so that you can copy the formula instead of editing for the others.

The cause didn't stand out easily, there is a bug either with the countifs function, or with my way of thinking how it should work in this scenario

I'm going to look into that more and see what I can find, meanwhile an alternative that works

PHP Code: 

=SUM(SIGN(FREQUENCY(IF($A$2:$A$4000="Aaron",$B$2:$B$4000),IF($A$2:$A$4000="Aaron",$B$2:$B$4000)))) 


As before, Array confirmed with Shift Ctrl Enter.

I'm sure that's not the same method that most poeple use for FREQUENCY() formula, but it gives correct results

That looks like be working now with your new formula. Thank you!!