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

**Prof Brian Ripley
**
Prof Brian Ripley <ripley@stats.ox.ac.uk>

*Wed, 11 Aug 1999 13:57:01 +0100 (BST)*

>* 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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