[R] How to know created time of object in R?

[Prof Brian Ripley]

On Tue, 6 Nov 2007, Alberto Monteiro wrote:

>
> Prof Brian Ripley wrote:
>>
>>> I would like to know the created time and date of specific object.
>>> Is there any function for it?
>>
>> There isn't even the concept.  Most objects in R are a collection of
>> SEXPRECs created at different times.  Suppose you create a data
>> frame out of existing columns, and then later change the names? What
>> does 'created' mean for the data frame?
>>
>> In any case, none of the possibly relevant date-times is stored.
>>
> I imagine that it could be possible to create a class that
> would store the "creation time" of its objects... but I have
> no idea how to do it (I think I could do it in C++, but I am
> illiterate in R++ oops S4 classes).

You could record the time at which you recorded the time by e.g.

attr(x, "creation time") <- Sys.time()

but this would be subject to all the ambiguities I mentioned.  For an S4 
class you could have a slot for time and assign it in the constructor, but 
it is commonplace to use new() to create a skeleton object and then fill 
it in.  You would then need to arrange for all the subset and 
subassignment methods to either preserve or update the time.

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595