Create a unique ID for multiple diagnosis

Hi

I have a very large data set, which involves unique IDs for participants, but each ID is repeated every time the participants are diagnosed with a condition. Looks a bit like this:


ParticipantID DiagnosisCode Date
1 3fe 23apr2010
1 4rt 30mar2009
2 43e 01apr2011
2 2qw 09may2012
3 5yh 10jun2011
3 6ty 08jul2013

How do I create a unique ID which lists the number of diagnosis codes per child as the dates associated with diagnosis. Do I need to use wide format to do this or can it be done in long?

Thanks a lot

Luca