[R] date/time arithmetic

[bogdan romocea]

What do you need a bunch of functions for? I'm not familiar with the
details of difftime objects, however an easy way out of here is to get
the time difference in seconds, which you can then add or subtract as
you please from date-times.

x<-Sys.time(); y<-Sys.time()+3600
diff <- as.numeric(difftime(y,x,units="secs"))
x; y; diff
y-diff


> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch
> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of
> Parlamis Franklin
> Sent: Wednesday, November 30, 2005 1:57 PM
> To: Parlamis Franklin
> Cc: r-help at stat.math.ethz.ch
> Subject: Re: [R] date/time arithmetic
>
>
> Hi.  Sorry to pester, but I didn't get a reply to this
> (perhaps owing
> to Thanksgiving break).  This seems to be a case where the R
> language
> simply doesn't do what it says it does (i.e., allow addition or
> subtraction of a difftime object and a date-time object).
>
> Am I wrong?  I am about to write a bunch of functions (easy, but
> perhaps redundant) to do this, and I just want to know whether there
> is a bug here, or whether I am missing something obvious.
>
> Thanks.
>
> FP
>
> On Nov 23, 2005, at 10:02 AM, Parlamis Franklin 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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