[R] Selecting the first measurement only from a longitudinal sequence

From: john james <dntssa_at_yahoo.com>
Date: Fri, 25 Jul 2008 12:31:32 -0700 (PDT)


Dear R-help mailing list,
 

I have this problem, I have a joint  longitudinal and survival data of the form say
 

ID Time Failuretime Censoringind longitudinalmeasure

1  0     35                  0                123
1  10    35                 0                 120 
1   25   35                 1                   123
2   0    23                  0                   100
2   10  23                  0                   111

 
 

I wish to create a new dataset such that only the first measurement is included.
 

Also, i will appreciate if there is a function that i could call to do this because I will be applying it too in a simulation settings.
 

Thank you for your time.
 
James.                


      
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