Count of unique values based on two columns of data

I have a spreadsheet that is completed by a foreman for work completed in a given week. Multiple foreman can work on a job in a given week. I want to determine the number of foreman that worked on a job for each week.

Example would be

Column K Column M

7540 03/04/12
7540 03/11/12
6280 03/11/12
6281 03/11/12
7540 03/18/12
6280 03/18/12


I am only using week ending dates (Sundays) and each forman has a unique id (employee ID) that is being used on the report.

Column K is where the employee's id is recorded and Column M is the week ending. In the example above, I want a formula that will give me a count of three for the weekending 03/11/12 and a count of two for weekending 03/18/12

My first post so be patient with me.

Thanks,
Jody

Assuming your data is in rows 1-6, with the date value you're looking for in A1 then try this:

=SUM(--(IFERROR(MATCH(K1:K6,INDEX(K1:K6*(M1:M6=A1),0),0),-99)=ROW(K1:K6)))

This is an array formula, so must be entered using Ctrl-Shift-Enter, not just Enter.

{ shows up at the beginning fo the formula box, but gives me a result of "True"

The { should show up, that indicates you've added it as an array formula, so that's fine.

I can't see how it could return a value of TRUE, however. Is it possible for you to post an example workbook?

Let's see if this posts

Somehow the formula has ended up in the cell twice. If you delete the entire contents of that cell and then paste in the formula again it should work.

Sweet. Thank you.

I wonder if you could help me with a similar formula, however in column K i have names of clients and in column M i have the months of the year expressed as a numeric value. I want to count the unique values in column K in an individual month.

I may want to add in further criteria for Quarter and Year, but I'm sure that once the first formula is figured out i can work to adapt it. I have a separate summary table which reference and i have support columns for Month, Quarter and Year.