Count from last timestamp?

[#1]

How do you create an expression to get a count of last timestamp of ID for each LEVEL and RISK from the table below?

TIMESTAMP	ID	LEVEL	RISK
7/23/2012	1264	9	6
7/24/2012	1288	9	5
7/24/2012	1357	2	6
7/24/2012	1357	2	6
7/24/2012	1833	1	6
7/25/2012	1366	2	6
7/26/2012	1222	9	4
7/27/2012	1222	3	6
7/28/2012	2889	2	6
7/30/2012	2889	2	6
7/31/2012	6777	2	6

I would expect to get the following counts:

LEVEL=1 RISK=6 ====> COUNT=1

LEVEL=2 RISK=6 ====> COUNT=4

etc...

[#2]

try:

count(aggr(max(TIMESTAMP),ID,LEVEL,RISK))

[#3]

I need to add one more step, how would I update this expression if I wanted to count only if LEVEL=2?

[Gysbert_Wassenaar]

try: count(aggr(max({$<[LEVEL]={'2'}>} TIMESTAMP),ID,LEVEL,RISK))

[#5]

Thank you this works now!

[#6]

Thank you this works now!

[#7]

Thank you this works now!