Re: ts and defaults

About this list Date view Thread view Subject view Author view Other groups

Subject: Re: ts and defaults
From: Prof Brian D Ripley (ripley@stats.ox.ac.uk)
Date: Sat 07 Aug 1999 - 05:55:21 EST


Message-ID: <Pine.GSO.4.05.9908062019540.20236-100000@auk.stats>

On Fri, 6 Aug 1999, Paul Gilbert wrote:

> Brian
>
> The example below may be helpful to further illustrate the concern I have with
> the effects of your ts library on defaults. According to the "Blue Book", in
> Splus, in R up to 0.64.2, and in today's snapshot of 0.65 without the "ts"
> library attached
>
> > end(ts(rnorm(10), start=c(1991,1), frequency=1))
>
> gives
> [1] 2000 1

How is anyone supposed to know that means 2000 not 2001 without reading
the help page?

> However, with the "ts" library attached the result is
>
> [1] 2000

Isn't that much more readable?

> This change in the default behavior will break a lot of user code [ ... ]

Statistical evidence, please.

Note that all the S (and R) code is written to accept start=1991, so this
user code must depart from that convention. Maybe it would be a good
opportunity to re-write that code to conform to the standard conventions?
As in

start: starting date for the series, e.g., in years, February,
       1970 would be 1970+(1/12) or 1970.083. If start is a
       vector with at least two data values, the first is
       interpreted as the time unit, e.g., the year, and the
       second as the number of positions into the sampling
       period; e.g., February, 1970 could be c(1970,2).

Note the two possibilities, and that the one you advocate is the
alternate. I at least find c(1970, 2) = 1970+(1/12) a _very_ confusing
notation, fortunately one that can be avoided.

The problem here is that ts in R is fundamentally incompatible with S, as R
has a ts class and S does not. I believe start.default should not be
implemented in terms of class ts (and any user can change the
behaviour of a class), and I trust the `lots of user code' does not do
things like that. The plan is to separate the the default methods from the
ts class methods. We do not consider that S compatibility applies
to class ts, which S does not have.

Brian

-- 
Brian D. Ripley,                  ripley@stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-devel mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-devel-request@stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._


About this list Date view Thread view Subject view Author view Other groups

This archive was generated by hypermail 2b25 : Tue 04 Jan 2000 - 14:16:07 EST