Determining date of last occurance for panal data

Hi,

I have data organised by participant ID and episode ID for specific occurrences. I am having trouble determining the date of last occurrence for each participant (for determining person years for followup). My data looks a bit like this:

Participant_ID Episode_ID Date
1 1_1 01 Jan 10
1 1_2 etc
1 1_3
2 2_1
3 3_1
3 3_2
4 4_1
4 4_2
4 4_3
4 4_4
etc

Thanks, any help is much appreciated.