[Rd] [R] New errors with difftime()-objects in 2.11.1 (was Re: Request: difftime method for cut())

Gustaf Rydevik gustaf.rydevik at gmail.com
Wed Jun 23 10:57:56 CEST 2010

On Wed, Jun 23, 2010 at 7:13 AM, Peter Dalgaard <pdalgd at gmail.com> wrote:
> Gustaf Rydevik wrote:
>> Oh, I forgot to mention that the workaround of using as.double (or
>> as.numeric) works fine, and I've done that.
>> It's just that it can take quite a while (as in several hours) to
>> figure out that the reason for the error is that you have to force
>> difftime objects to be numeric in 2.11.1, when the code's been working
>> fine before and the error messages are obscure.
> I don't think you realize the problems that could occur by assuming that
> difftime objects are numerics ON ANY PARTICULAR SCALE!
> --
> Peter Dalgaard
> Center for Statistics, Copenhagen Business School
> Phone: (+45)38153501
> Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com

Ah. Yes, you're right that it would be problematic to say the least to
assume that the difftime object is measured in days and not in, say,
seconds. And I suppose that it makes sense to prioritize avoiding
calculations that give misleading results over forcing changes in old
code.  I was just caught somewhat unprepared, and I know that my
colleagues  who is not quite as R-literate will be even more
unprepared for old stuff no longer working.
Usually, R prepares the user for these kind of things by throwing
warnings a version or two before the change is actually implemented.
But I guess that's not always practical.

I take it that your argument would also work agains implementing
simple difftime-methods of functions as well, where you force difftime
objectws to be numeric? In that case, people can disregard my
suggestion of adding a difftime-method to cut().

Anyhow, I'll stop whining now. Thanks for the good work you're doing
in the R Core team.


Gustaf Rydevik, M.Sci.
tel: +46(0)703 051 451
address:Essingetorget 40,112 66 Stockholm, SE

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