Re: [R] Age of an object?

From: Duncan Temple Lang <duncan_at_wald.ucdavis.edu>
Date: Thu 15 Dec 2005 - 01:37:27 EST

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Roger Bivand wrote:

> On Wed, 14 Dec 2005, Martin Maechler wrote:
> 
> 

>>>>>>>"Kjetil" == Kjetil Brinchmann Halvorsen <kjetilbrinchmannhalvorsen@gmail.com>
>>>>>>> on Wed, 14 Dec 2005 08:59:24 -0400 writes:
>>
>> Kjetil> Philippe Grosjean wrote:
>> >> Martin Maechler wrote:
>> >>>>>>>> "Trevor" == Trevor Hastie <hastie@stanford.edu>
>> >>>>>>>> on Tue, 13 Dec 2005 12:51:34 -0800 writes:
>> >>>
>> Trevor> It would be nice to have a date stamp on an object.
>>
>> Kjetil> Following up on my post of a few minutes ago, I tried to write an
>> Kjetil> timestamp function
>>
>> Kjetil> timestamp <- function(obj, moretext){
>> Kjetil> comment(obj) <<- paste(Sys.time(), moretext, sep="\n")
>> Kjetil> }
>>
>> Kjetil> but this does'nt work.
>>
>> >> myobj <- 1:10
>> >> timestamp(myobj, "test")
>> Kjetil> Error in timestamp(myobj, "test") : object "obj" not found
>> >>
>>
>>Instead, I'd **strongly** recommend to define *two* functions,
>>one "constructor" and one "inspector" :
>>
>>"timestamp<-" <- function(obj, value) {
>> stamp <- paste(Sys.time(), value)
>> ## attr(obj,"timestamp") <- stamp
>> comment(obj) <- stamp
>> obj
>>}
> 
> 
> This does treat any existing comment rather brutally, could stamp rather 
> be:
> 
>     stamp <- paste(Sys.time(), comment(obj), value)
> 
> probably enhanced with some field separators to let the inspector grab 
> just its chunk? Something like DCF?


Why not use a regular named vector/list rather than pasting things into and then back from a string, relying on conventions and losing information.

   current <- comment(obj)
   current[["timeStamp"]] <- Sys.time()
   comment(x) <- current

and then the individual elements can be accessed in the usual manner

   comment(x)[["timeStamp"]]
and the original value can be be maintained (with a little more tinkering for old-style cases without named elements).

> 
> 

>>## and
>>
>>timestamp <- function(obj) {
>> ## attr(obj,"timestamp")
>> comment(obj)
>>}
>>
>>## and the usage (shown with output)
>>
>>myobj <- 1:9
>>timestamp(myobj) <- "as an example"
>>
>>myobj
>>## 1 2 3 4 5 6 7 8 9
>>timestamp(myobj)
>>## "2005-12-14 14:57:33 as an example"
>>
>>-------
>>
>>we had mentioned recently here that "good programming style"
>>works with functions that do *not* modify other objects but
>>rather *return*..
>>
>>
>>
>> >>>
>> Trevor> In S/Splus this was always available, because objects were files.
>> >>>
>> >>> [are you sure about "always available"?
>> >>> In any case, objects were not single files anymore for a
>> >>> long time, at least for S+ on windows, and AFAIK also on
>> >>> unixy versions recently ]
>> >>>
>> >>> This topic has come up before.
>> >>> IIRC, the answer was that for many of us it doesn't make sense
>> >>> most of the time:
>> >>
>> >> I remember it was discussed several times. I don't remember why it was
>> >> considered too difficult to do.
>> >>
>> >>> If you work with *.R files ('scripts') in order to ensure
>> >>> reproducibility, you will rerun -- often source() -- these files,
>> >>> and the age of the script file is really more interesting.
>> >>> Also, I *always* use the equivalent of q(save = "no") and
>> >>> almost only use save() to particularly save the results of
>> >>> expensive computations {often, simulations}.
>> >>
>> >> OK, now let me give examples where having such an information would ease
>> >> the work greatly: you have a (graphical) view of the content of an
>> >> object (for instance, the one using the "view" button in R commander),
>> >> or you have a graphical object explorer that has a cache to speed up
>> >> display of information about objects in a given workspace (for instance,
>> >> the SciViews-R object explorer). What a wonderful feature it will be to
>> >> tell if an object was changed since last query. In the view, one could
>> >> have a visual clue if it is up-to-date or not. In the object explorer, I
>> >> could update information only for objects that have changed...
>> >>
>> Trevor> I have looked around, but I presume this information is not available.
>> >>>
>> >>> I assume you will get other answers, more useful to you, which
>> >>> will be based on a class of objects which carry an
>> >>> 'creation-time' attribute.
>> >>
>> >> Yes, but that would work only for objects designed that way, and only if
>> >> the methods that manipulate that object do the required housework to
>> >> update the 'last-changed' attribute (the question was about last access
>> >> of an object, not about its creation date, so 'last-changed' is a better
>> >> attribute here). If you access the object directly with, let's say,
>> >> myobject@myslot <- newvalue, that attribute is not updated, isn't it?
>> >>
>> >> Best,
>> >>
>> >> Philippe Grosjean
>> >>
>> >>> Martin Maechler, ETH Zurich
>> >>>
>>
>>______________________________________________
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>>
>
>

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R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Thu Dec 15 01:49:49 2005

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