[R] Age of an object?

[Roger Bivand]

On Wed, 14 Dec 2005, Martin Maechler wrote:

> >>>>> "Kjetil" == Kjetil Brinchmann Halvorsen <kjetilbrinchmannhalvorsen at gmail.com>
> >>>>>     on Wed, 14 Dec 2005 08:59:24 -0400 writes:
> 
>     Kjetil> Philippe Grosjean wrote:
>     >> Martin Maechler wrote:
>     >>>>>>>> "Trevor" == Trevor Hastie <hastie at 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?

> 
> ## 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 at myslot <- newvalue, that attribute is not updated, isn't it?
>     >> 
>     >> Best,
>     >> 
>     >> Philippe Grosjean
>     >> 
>     >>> Martin Maechler, ETH Zurich
>     >>>
> 
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-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no