On the help page "DateTimeClasses {base}" it says:

"One can add or subtract a number of seconds or a difftime object  
from a date-time object, but not add two date-time objects."

However,

 > x<-Sys.time(); y<-Sys.time()+3600
 > diff<-y-x
 > x; y; diff
[1] "2005-11-23 19:58:20 GMT"
[1] "2005-11-23 20:58:20 GMT"
Time difference of 1 hours
 > y-diff
[1] "2005-11-23 20:58:19 GMT"
Warning message:
Incompatible methods ("-.POSIXt", "Ops.difftime") for "-"

Do I have the syntax wrong?  Or is some conversion of the difftime  
object to raw seconds necessary prior to performing arithmetic?  And  
is the help page wrong?

Thanks.

Franklin





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