On Wed, 2008-12-03 at 13:18 -0500, Gabor Grothendieck wrote: > What is odd is that it seems to run ok if we call "+.Date" directly: > > > "+.Date"(alpha1, alpha2) > [1] "2009-02-15"
It also works if you flip the ordering: > alpha2 + alpha1 [1] "2009-02-15" Warning message: Incompatible methods ("+.Date", "Ops.difftime") for "+" It is just a warning, but one should check that the answer is correct given the perceived problem with different classes of objects. Why it works is not odd if you look at the help for ?`+.Date`, which shows that for this method (correct term?) we need 'date' + 'x', where 'date' is an object of class Date and 'x' is numeric. The OP can avoid the warning by: > alpha2 + as.numeric(alpha1) [1] "2009-02-15" If you put alpha1 first (class difftime) that method gets used and alpha2 is coerced to numeric to complete the operation: > alpha1+alpha2 Time difference of 14290 days Warning message: Incompatible methods ("Ops.difftime", "+.Date") for "+" > as.numeric(alpha2) + 56 [1] 14290 To answer the OP's question about conversion, no you don't need to convert Date objects to numerics to work with them. You just need to be aware of method dispatch for `+()` and check that adding objects of differing classes makes sense. Of course, this assumes that the OP wanted the answer as an object of class "Date"...? G > > On Tue, Dec 2, 2008 at 4:10 PM, Christophe Dutang <[EMAIL PROTECTED]> wrote: > > Hi all, > > > > I'm dealing with dates in R (2.7.2), but some basic operations raise a > > warning. > > > > Incompatible methods ("+.Date", "Ops.difftime") for "+" > > > > I saw this topic in this mailing list, but I do not understand what to > > do... > > > > cf. https://stat.ethz.ch/pipermail/r-help/2008-June/165842.html > > > > Do I have to convert Dates to numeric? > > > > Thanks in advance > > > > Christophe > > > > PS : R script used > > > > alpha2=as.Date("2008-12-21") > > alpha1=as.Date("2008-12-21")-as.Date("2008-10-26") > > alpha1 > > alpha2 > > alpha1+alpha2 > > > > > > [[alternative HTML version deleted]] > > > > ______________________________________________ > > R-help@r-project.org mailing list > > https://stat.ethz.ch/mailman/listinfo/r-help > > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > > and provide commented, minimal, self-contained, reproducible code. > > > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. -- %~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~% Dr. Gavin Simpson [t] +44 (0)20 7679 0522 ECRC, UCL Geography, [f] +44 (0)20 7679 0565 Pearson Building, [e] gavin.simpsonATNOSPAMucl.ac.uk Gower Street, London [w] http://www.ucl.ac.uk/~ucfagls/ UK. WC1E 6BT. [w] http://www.freshwaters.org.uk %~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%
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______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.