[R] Incompatible methods ("+.Date", "Ops.difftime") for "+"

From: Richard M. Heiberger <rmh_at_temple.edu>
Date: Wed, 25 Jun 2008 00:23:38 -0400 (EDT)

I received a warning about incompatible methods that I don't understand. The workaround in this example is simple.

What is the reason that these methods are seen as incompatible? Is there some dangerous consequence of my as.numeric() workaround? Can a fix to the code base, perhaps similar to my workaround, make this warning no longer necessary?

I am using R 2.7.0 on Windows.
version.string R version 2.7.0 (2008-04-22)



xlim <- as.Date(c("2005-04-09", "2007-09-07")) dx <- diff(xlim)
xlim + c(-.02, .02)*dx ## correct answer and warning message xlim + as.numeric(c(-.02, .02)*dx) ## correct answer

> xlim <- as.Date(c("2005-04-09", "2007-09-07"))
> xlim

[1] "2005-04-09" "2007-09-07"
> dx <- diff(xlim)
> dx

Time difference of 881 days
> xlim + c(-.02, .02)*dx ## correct answer and warning message
[1] "2005-03-22" "2007-09-24"
Warning message:
Incompatible methods ("+.Date", "Ops.difftime") for "+"
> xlim + as.numeric(c(-.02, .02)*dx) ## correct answer
[1] "2005-03-22" "2007-09-24"

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