Hi I am working with a dataset which ahs multiple dates for the same diagnosis for a patient and I only want to keep the observations with the earliest date and drop the rest. I am going to explain a bit how the dataset is so that it can be understandable.

ID DIAGNOSIS DATE
1 CKD 2/9/2000
1 CKD 4/7/2008
1 CHF 2/5/2005
1 CHF 5/5/2009

What I want it to like is to have a column of diagnosis and only the first date.
Please help me out. Thanks

Ushma