[R] Aggregate by First case

From: Jojje Andersson <dietaamigo_at_hotmail.com>
Date: Fri, 30 May 2008 09:13:19 +0200


I have an maybe a to a simple question but I cant get it right.  

I have a dataframe with in one column an id-variable and in another a year-variable. One id-number can occur several years. I have sorted the dataframe on id then on year so the same id-number is sorted by year with the first occurens at top.  

Now I want to make a subset of this dataframe with just the first year the id-number occur, so the first case of every id.  

Id Year
123456 2001
123456 2002
123456 2003
655432 2001
655432 2002
655432 2003  

Is there a simple command I can do?  



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