Is a ts of length one a ts? (PR#245)

[Prof Brian Ripley]

> Date: Wed, 11 Aug 1999 13:52:51 +0200 (CEST)
> From: Martyn Plummer <plummer@iarc.fr>
> To: Prof Brian D Ripley <ripley@stats.ox.ac.uk>
> Subject: RE: Is a ts of length one a ts? (PR#245)
> Cc: r-devel@stat.math.ethz.ch, R-bugs@biostat.ku.dk
> 
> On 11-Aug-99 Prof Brian D Ripley wrote:
> > On Wed, 11 Aug 1999, Martyn Plummer wrote:
> > 
> >> On 10-Aug-99 ripley@stats.ox.ac.uk wrote:
> >> > Is there any good reason why a time series of length one is not
> >> > allowed by [.ts (you can certainly create one with ts)?
> >> 
> >> It certainly has a start and an end value, but what's the
> >> frequency?  If you want the tsp attribute of a time series
> >> to be well defined, then maybe you should disallow series
> >> of length 1.
> > 
> > I think the frequency is perfectly well defined, as that of the series you
> > subsetted.
> 
> Is it?
> 
> R 0.64.2:
> 
> R> x <- ts(1:10)
> R> frequency(x)
> [1] 1
> R> y <- x[c(2,4,6,8,10)]
> R> frequency(y)
> [1] 0.5
> 

I was only discussing the case of a subset of one, but you omitted
the next sentence. What I actually said was

`I think the frequency is perfectly well defined, as that of the series you
subsetted.  How can extracting one observation change the frequency of
observation?'

Obviously, subsetting a regularly spaced series can change the frequency.
 
-- 
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

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