[R] date/time arithmetic

[Gabor Grothendieck]

I don't know what is wrong but you could use the numeric class
instead of the difftime class as a workaround:

x <- Sys.time()
y <- x + 3600
diffyx <- as.numeric(y) - as.numeric(x)
identical(y - diffyx, x) # TRUE

On 11/23/05, Parlamis Franklin <fparlamis at mac.com> wrote:
> 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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