[R] Age of an object?

[Henrik Bengtsson]

If R would have timestamps telling when any object was last modified, we 
could extend R with a 'GNU make'-style functionality (or syntax) 
together with some fancy caching to persistent storage (files, data 
bases, ...).  That would really nice!  As B.R. and M.M. writes, 
timestamping is most suited for higher level data structures and not 
simple data types, because the over head would be too large.

/Henrik


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.
>>
>>    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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