[R] Data frame which includes a non-existent date

[Frank S.]

Hi to all members of the list,
 
I have a data frame with subjects who can get into a certain study from 2010-01-01 onwards. Small example:
 
DF <- data.frame(id=as.factor(1:3), born=as.Date(c("1939/10/28", "1946/02/23", "1948/02/29")))

  id       born
1  1 1939-10-28
2  2 1946-02-23
3  3 1948-02-29
 
Now, I add a new column "enter" as follows:
 
1) If the subject is 65 years old before 2010-01-01, then enter=2010-01-01.
2) If the subject i NOT 65 years old before 2010-01-01, then enter="Date on which subject reach 65"
 
DF_new <- data.frame(DF, 
 enter= as.Date( ifelse(unclass(round(difftime(open, DF$born)/365.25,1))<=65,
paste(year(DF$born)+65,substr(DF$born,6,10),sep="-"), paste(open))) )
 
The problem is that the DF_new output has a NA in subject id=3:
 
  id       born      enter
1  1 1939-10-28 2010-01-01
2  2 1946-02-23 2011-02-23
3  3 1948-02-29       <NA>
 
I'm afraid (I'm not really sure) that the matter is that subject id=3 would reach 65 yr at 2013-02-29, but this date does not exist,
so R gives a missing.
 
Can any help me?
 
Thank you!!!
 
 
 
 
 		 	   		   		 	   		  
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