[R] Adding meta-data when creating objects. e.g: changing "<-" so to (for example) add "creation time" - how-to and pros/cons?

[Ivan Calandra]

Hi Michael,

I had already seen your solution (that does work).
If you're right about the issue in "my" function, then the error message 
is confusing ('could not find the function "get<-" '). Moreover, I 
assign()ed and get() "x" from the .GlobalEnv, so there shouldn't be a 
problem with scoping, right?

It's just that R doesn't behave as I expect, so I'd like to understand 
where I'm wrong.

Thanks again for any hints!

Ivan



Le 11/12/2010 02:55, Michael Bedward a écrit :
> Hi Ivan,
>
> It doesn't work because there is no object called "x" in the
> function's local scope.
>
> Try this...
>
> function(x, ...) {
>   xname<- deparse(substitute(x))
>   assign(xname, ...)
>   x<- get(xname)
>   attr(x, "creation.time")<- Sys.time()
>   assign(xname, x, pos=.GlobalEnv)
> }
>
> Michael
>
>
> On 11 November 2010 22:17, Ivan Calandra<ivan.calandra at uni-hamburg.de>  wrote:
>> Hi,
>>
>> I have tried this (just to practice):
>> assign2<- function(x, ...){
>>   assign(x, ..., envir=.GlobalEnv)
>>   attr(get(x, envir=.GlobalEnv), "creation.time")<- Sys.time()
>> }
>>
>> assign2("y", 1:4)
>> Error in attr(get(x), "creation.time")<- Sys.time() :
>>   could not find function "get<-"
>>
>> Why doesn't it work?
>> If I remove the attr() part,
>> identical(y, get("y")) returns TRUE, so why attr() cannot work with it?
>>
>> Thanks in advance for the clarification,
>>
>> Ivan
>>
>>
>> Le 11/11/2010 11:16, Michael Bedward a écrit :
>>> Hi Tal,
>>>
>>> Here's a way of doing the first bit...
>>>
>>> assign2<- function(x, ...) {
>>>    xname<- deparse(substitute(x))
>>>    assign(xname, ...)
>>>    x<- get(xname)
>>>    attr(x, "creation.time")<- Sys.time()
>>>    assign(xname, x, pos=.GlobalEnv)
>>> }
>>>
>>> Michael
>>>
>>>
>>> On 11 November 2010 20:37, Tal Galili<tal.galili at gmail.com>    wrote:
>>>> My objective is to start having meta-data on objects that I create.
>>>> For example, consider the following function:
>>>>
>>>> assign2<- function(x, ...)
>>>> {
>>>>   assign("x", ...)
>>>> attr(x, "creation time")<- Sys.time()
>>>>   x<<- x
>>>> }
>>>>
>>>> assign2("x", 1:4)
>>>>
>>>> "assign2" assigns to x the vector 1:4, and it then also adds the creation
>>>> time of the object.
>>>>
>>>> (Hat tip goes to Peter Alspach for pointing me to the concept of adding
>>>> meta
>>>> data to an object using attr)
>>>>
>>>>
>>>> But this function has several major limitations:
>>>> 1) It will not work for any assignment other then "x".  For example
>>>> assign2("y", 1:4)
>>>> Doesn't work.
>>>> How might this be fixed ?
>>>> 2) This function will probably need to also search the parent environment
>>>> if
>>>> the variable already exists.  If it does, then there should be a "update
>>>> date" instead of "creation date".  But for that to work, I'll need a
>>>> solution for problem 1.
>>>> 3) How will this handle a case when we are updating only a subset of the
>>>> items?  (for example:  assign2("x[1:2]", 8:9) )
>>>> 4) My real intention is to somehow change the "<-" operator (not simply
>>>> the
>>>> assign).  I am unsure as to how to do that.
>>>> 5) Are there any major pros/cons to the adding of such meta-data to
>>>> objects?
>>>> (for example, excessive overhead on memory/performance)
>>>> 6) Is there already some system that knows how to do this in R (which I
>>>> am
>>>> simply ignorant about)?
>>>>
>>>> Thanks for following through, and for any suggestions/thoughts you might
>>>> have.
>>>>
>>>> Best,
>>>> Tal
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> ----------------Contact
>>>> Details:-------------------------------------------------------
>>>> Contact me: Tal.Galili at gmail.com |  972-52-7275845
>>>> Read me: www.talgalili.com (Hebrew) | www.biostatistics.co.il (Hebrew) |
>>>> www.r-statistics.com (English)
>>>>
>>>> ----------------------------------------------------------------------------------------------
>>>>
>>>>         [[alternative HTML version deleted]]
>>>>
>>>> ______________________________________________
>>>> R-help at r-project.org mailing list
>>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>>> PLEASE do read the posting guide
>>>> http://www.R-project.org/posting-guide.html
>>>> and provide commented, minimal, self-contained, reproducible code.
>>>>
>>> ______________________________________________
>>> R-help at r-project.org mailing list
>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>> PLEASE do read the posting guide
>>> http://www.R-project.org/posting-guide.html
>>> and provide commented, minimal, self-contained, reproducible code.
>>>
>> --
>> Ivan CALANDRA
>> PhD Student
>> University of Hamburg
>> Biozentrum Grindel und Zoologisches Museum
>> Abt. Säugetiere
>> Martin-Luther-King-Platz 3
>> D-20146 Hamburg, GERMANY
>> +49(0)40 42838 6231
>> ivan.calandra at uni-hamburg.de
>>
>> **********
>> http://www.for771.uni-bonn.de
>> http://webapp5.rrz.uni-hamburg.de/mammals/eng/mitarbeiter.php
>>
>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>

-- 
Ivan CALANDRA
PhD Student
University of Hamburg
Biozentrum Grindel und Zoologisches Museum
Abt. Säugetiere
Martin-Luther-King-Platz 3
D-20146 Hamburg, GERMANY
+49(0)40 42838 6231
ivan.calandra at uni-hamburg.de

**********
http://www.for771.uni-bonn.de
http://webapp5.rrz.uni-hamburg.de/mammals/eng/mitarbeiter.php