**Subject: **RE: Is a ts of length one a ts? (PR#245)

**From: **Martyn Plummer (*plummer@iarc.fr*)

**Date: **Wed 11 Aug 1999 - 21:52:51 EST

**Next message:**Prof Brian Ripley: "RE: Is a ts of length one a ts? (PR#245)"**Previous message:**Prof Brian D Ripley: "RE: Is a ts of length one a ts? (PR#245)"**In reply to:**Prof Brian D Ripley: "RE: Is a ts of length one a ts? (PR#245)"**Next in thread:**Prof Brian Ripley: "RE: Is a ts of length one a ts? (PR#245)"**Reply:**Martyn Plummer: "RE: Is a ts of length one a ts? (PR#245)"

Message-ID: <XFMail.990811135251.plummer@iarc.fr>

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

This agrees with the S-PLUS treatment of "regular" time series:

*S> x <- rts(1:10)
*

*S> frequency(x)
*

frequency

1

*S> y <- x[c(2,4,6,8,10)]
*

*S> frequency(y)
*

frequency

0.5

By this logic, the frequency of a single element selected from

a time series is undefined. S-PLUS can get round this problem

because it has the richer time series class "its":

*S> z <- x[1]
*

*S> class(z)
*

[1] "its"

So although z still has a time dimension, it has no frequency.

S-PLUS does allow you to create an "rts" object of length one. There is

a certain logic to this. The time series parameters must satisfy the

equation

frequency * (end - start) = length - 1

For a series of length 1:

frequency * 0 = 0

which is satisfied by any user-specified value of the frequency.

Martyn

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**Next message:**Prof Brian Ripley: "RE: Is a ts of length one a ts? (PR#245)"**Previous message:**Prof Brian D Ripley: "RE: Is a ts of length one a ts? (PR#245)"**In reply to:**Prof Brian D Ripley: "RE: Is a ts of length one a ts? (PR#245)"**Next in thread:**Prof Brian Ripley: "RE: Is a ts of length one a ts? (PR#245)"**Reply:**Martyn Plummer: "RE: Is a ts of length one a ts? (PR#245)"

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