[Rd] Saving nothing with save()

[Simon Urbanek]

Martin,

On Dec 19, 2011, at 6:39 AM, Martin Maechler wrote:

>>>>>> Barry Rowlingson <b.rowlingson at lancaster.ac.uk>
>>>>>>    on Sun, 18 Dec 2011 01:32:52 +0000 writes:
> 
>> Scenario: Here I am working away in R. I've got results
>> that prove global warming is anthropogenic and also the
>> solution for producing limitless carbon-neutral energy
>> from nuclear fusion. Its been a good day.
> 
>> So, I want to save my work. I don't want to overwrite my
>> current .RData, so I save it to another file:
> 
>> save(file="prize.RData") # just need to email this to the
>> Nobel committee q() Save workspace image? [y/n/c]: - "no"
>> I don't want to save the workspace image, I just saved
>> everything to "prize.RData". But gee, it did seem to do
>> that quite quickly considering the volume of evidential
>> data in my work. My unix shell prompt returns.
> 
>> Uh oh. See what I did there? I typed 'save' when I meant
>> 'save.image'.  What does that give me?
> 
>> A 42 byte, empty, latest.RData, and because there was no
>> warning or error I quit without saving it
>> again. Oops. Massive Data Loss.
> 
>> Is there any reason why save(file="file.RData") couldn't
>> warn or error if you try and save nothing? There's no
>> obvious check in the R code for save.
> 
>> Barry
> 
>> PS the above scenario is fictional.
> really?  ;-)
> 
> well, after *not* save()ing all your findings, it wouldn't have
> been such a good day, would it?
> 
> well, in spite of that.
> I agree that  save() should warn or stop in that case.
> I have now committed a version -- to R-devel only -- 
> which stop()s if  'pretest=TRUE' and uses  warning() otherwise,

I don't think I like that - why should it warn/stop in any case even when the use is absolutely legal?

I think this is the wrong approach - the whole idea was to warn on unintended *interactive* use - breaking existing code in the process is IMHO not necessary. I don't think 
save(list=x, file=y)
should fail even if x is empty - that makes it fail for completely legal code. What Barry was worried about was the interactive case of
save(file=x)
which should IMHO warn (there is a precedent for stopping as well - see tar - so I won't object).

I really see no reason for adding the pretest flag - it makes no sense since is warns anyway so it doesn't help at all. I would propose changing *only* the behavior of save(file=x) (to warn or stop - personally I prefer former) and not anything else.


> e.g., in the case of save.image() when there's nothing to save.
> 

Why should save.image() warn? Again, it causes unnecessary trouble for automated saving... empty workspace is probably even more common that using save(file=foo) ... If save() was fixed as above, that would be a non-issue.


> Thank you, Barry. for the suggestion!

Well, you did not follow his suggestion, though ;)

Cheers,
Simon


> Martin
> 
>> When did I last have a good day?
> 
> (I wish you more of those..)
> 
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