From plummer@iarc.fr  Thu Dec 11 10:02:05 1997
From: plummer@iarc.fr (Martyn Plummer)
Date: Thu, 11 Dec 1997 11:02:05 +0100 (MET)
Subject: R-alpha: "[.ts"  warning "Not returning time series.."
Message-ID: <XFMail.971211111648.plummer@iarc.fr>

On 11-Dec-97 maechler@stat.math.ethz.ch wrote:
>>>>>> "PaulG" == Paul Gilbert <pgilbert@bank-banque-canada.ca> writes:
>
>    PaulG> I have a class "tframe" with more specific classes indicating
>    PaulG> how time is being represented, such as
>
>    >> class(tframe(data))
>    PaulG> [1] "ts" "tframe"
>
>    PaulG> but now "[.ts" produces warning messages
>
>    >> tframe(data)[2]
>    PaulG> Warning: Not returning a time series object [1] 2006.25
>
>    PaulG> Even my simplest tests produce hundreds of lines of warnings, so
>    PaulG> I've commented out the line # warning("Not returning a time
>    PaulG> series object") in "[.ts". I'm not sure if this is the best
>    PaulG> solution, but something is necessary.
>
>I agree that this can be a pain.
>On the other hand, I think it can be very helpful to get this warning
>when you subscript a time-series and don't get one anymore.
>
>I think we want
> 1) No warning if only one element of a time-series is chosen
>       (however, even this is debatable:
>        Think of a function containing code
>               i <- !is.na(...) && a < b
>               result.ts <- my.ts[i]
>
>        wouldn't you want to be warned if `result.ts' is not a ts anymore? )
>
> 2) A warning otherwise -- which can be turned off ---
>    I propose to create an option (one of `options()') to handle this.
>
>Another -- maybe even better -- alternative :
>We introduce an argument
>                               drop = TRUE
>as for arrays.
>Then the warning would only happen in the case  drop = FALSE
>when it was really impossible to make an (equispaced) ts out of the
>subscripted one.

Sorry this is my fault. I suggested this code because the previous
version of [.ts<- did not allow you to subscript time series at all
without unclassing them.  The current version at least tries to preserve
time series objects.  I think what we really need is an irregular time
series class like the S-PLUS "its". Then array subscripting can do the
right thing, and do it silently. In the absence of such a class in R,
I put the warning in.  The message could be translated as "fix me", so
I'm glad you brought it up.

Martyn
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R-alpha: "[.ts" warning "Not returning time series.."
Martyn Plummer