[R] Age of an object?

[Kjetil Brinchmann Halvorsen]

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.

One way to do this with important objects is to use the comment function
(in package base)

comment(myobj) <- "made last sunday of 2005"

Kjetil


>>
>>     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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> 
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