[R] Dating Objects

[Paul Gilbert]

Barry Rowlingson wrote:

> Rolf Turner wrote:
> 
> 
>>	I don't follow what you aren't following ....  It seems to me
>>	to be an eminently reasonable thing to want to do.  Answers
>>	questions such as ``Was x modified since y was modified?''
> 
> 
>   I wanted to have some sort of 'make'-like functionality in R. 

Why not just use make and generate a sequence of targets that come from 
renaming the .RData file saved after each step.

Suppose
> you have some complicated analysis that depends on several variables. If 
> you change one of them, you might not want to redo all the parts of the 
> analyses that dont depend on that change. Integrating this with Sweave 
> would be another gem, since parts of your Sweave document that might 
> take a long time to run might not need to run again if you've only 
> changed something after that point. If it takes an hour to generate a 
> dataset and two seconds to plot it, and you've made a change to the 
> plot, you dont want to re-run the whole data generation again when you 
> weave your document.
> 
> 
>>	I think I would make the modification data an ***attribute***
>>	of the object, rather than sticking it in as a component.
>>	(The latter might mess up some vital aspect of the nature
>>	of the object.)
>>
>>	The problem is to remember to date stamp each object each
>>	time it is modified ....
> 
> 
>   A while ago I attacked this problem at the C-code level. I found out 
> where R made assignments and tacked on a 'modified' attribute to the 
> object at that point. However it was a quick hack and it broke R quite 
> badly. One of the problems was that R objects were no longer identical 
> to assigned versions of themselves, and lots of tests broke.
> 
>   I think to be done properly it needs to be done at a lower level.

Well, I guess what I'm suggesting is at a much higher level.

Paul
> 
> Barry
> 
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