[Rd] RFC: Redefining length(<POSIXlt>) ?

Gregor Gorjanc gregor.gorjanc at bfro.uni-lj.si
Mon Jul 24 14:48:14 CEST 2006


Martin Maechler <maechler <at> stat.math.ethz.ch> writes:

> So I did open a new subject and move the discussion to R-devel
> now.
> >>>>> "MM" == Martin Maechler <maechler <at> stat.math.ethz.ch>
> >>>>>     on Mon, 24 Jul 2006 11:46:05 +0200 writes:
>   >>>>> "Gabor" == Gabor Grothendieck <ggrothendieck <at> gmail.com>
>   >>>>>     on Sun, 23 Jul 2006 09:02:35 -0400 writes:
>       Gabor> Looking at the diff.POSIXt code we see the problem is
>       Gabor> that it takes the length of the input using length
>       Gabor> which is wrong since in the case of POSIXlt the
>       Gabor> length is always 9 (or maybe length should be defined
>       Gabor> differently for POSIXlt?).
>     MM> Though I agree with Spencer that a user may expect
>     MM> length() to behave differently, but I don't think this
>     MM> would be a good idea.  Yes, length() is generic, but its
>     MM> help() emphasizes that for lists, length() should be the
>     MM> number of list elements.  Of course anyone one *can*
>     MM> define length() methods that behave differently for
>     MM> his/her classes, but then one would also want to make
>     MM> sure that e.g.  x[length(x)] or 'x[length(x)] <- value'
>     MM> works and -- in a case of simple S3 class built on a
>     MM> list, would work differently than if x was a the simple list.

I think that having generic for POSIXlt would be more natural than default
length, which is (as stated by Gabor) always 9. When I see a date or time with
all additions I always think of it as one "element". So it would be naturaly
that length() would return number of dates/times in POSIXlt object.


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