[R] Using POSIX?t rather than "chron" or "date"

Aleksey Naumov naumov at buffalo.edu
Thu Sep 18 18:55:17 CEST 2003

I agree with this. I am also in a situation where I need only dates (no
need for timezones or daylight saving time), and times actually get in a
way, complicating code and creating a mess. I've had occasions when
seq.POSIXt() did not work for me (could not generate a simple daily
sequence) due to the time component, which I don't need and never
specified. Even just the display of time component ("2002-10-20 08:00:00
EDT" vs. "2002-10-20") makes dates bulky and hard to track.

I also converted one of my date related function to chron and see much
improvement in code readability and reliability. On the one hand, I'd like
to stay with R base and not introduce another library dependency, however
chron provides the level of clarity beyond POSIXt classes (this
goes for function naming as well: chron(), dates(), times() are easier to
remember then strftime(), strptime() ...)

Don't have a remedy to offer, I'll leave this to more experienced users.
Just my 2c .

Best regards,

On Wed, 17 Sep 2003, Gabor Grothendieck wrote:

> The problem with POSIXt is that you must consider timezones 
> and daylight vs.  standard time issues even if you don't want 
> to.  This violates modularity (viz. your routines becomes coupled 
> to unrelated information) and leads to subtle errors where different 
> routines are assuming different time zones.
> The problem is that the time, date, day of the week, month, etc. 
> of a date depend on its time zone so even if you are just concerned 
> with daily data in a fixed time zone, say, you are still dragged 
> into time zone and standard vs. daylight considerations.
> I recently converted a program using POSIXt to chron and it allowed 
> me to eliminate all the tz parameters that I was passing around and 
> even better it meant I did not even have to THINK about time zones 
> and all the associated headaches they were giving me.
> I had previously suggested that we either put chron into the base 
> or create a new timezone-less version of POSIXt to complement what 
> is already in the base.  See:
> https://stat.ethz.ch/pipermail/r-devel/2003-August/027269.html
> --- Martin Maechler <maechler at stat.math.ethz.ch> wrote:
> >>>>> "BDR" == Prof Brian Ripley <ripley at stats.ox.ac.uk>
> >>>>>     on Wed, 17 Sep 2003 06:58:48 +0100 (BST) writes:
>     BDR> On Tue, 16 Sep 2003, Deepayan Sarkar wrote:
>     >> Is the date class standard enough to warrant including a
>     >> check for it in lattice ?
>     BDR> I don't think so.  The POSIX*t classes in R are the
>     BDR> most standard, followed by the chron package and only
>     BDR> then the date package.
> Definitely.  And I think we should encourage people to
> upgrade to POSIX.t from "chron" (let alone "date") more
> strongly {Note that there have been  as.POSIXct() methods for
> these classes since the beginning of the POSIX.t classes.
> Could "chron" and "date" users be heard about what
> functionality they are missing in POSIX.t ?
> On the other hand, the recommended package "survival" has
> a(nother?) class "date" and that package is based on S(plus) code
> and may hence not be convertible sensibly ?
> Martin Maechler <maechler at stat.math.ethz.ch>	http://stat.ethz.ch/~maechler/
> Seminar fuer Statistik, ETH-Zentrum  LEO C16	Leonhardstr. 27
> ETH (Federal Inst. Technology)	8092 Zurich	SWITZERLAND
> phone: x-41-1-632-3408		fax: ...-1228			<><
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