R help - May 2006 - How to make attributes persist after indexing?

On Wed, 2006-05-24 at 17:20 +0100, Heinz Tuechler wrote:
> Dear All!
> 
> For descriptive purposes I would like to add attributes to objects. These
> attributes should be kept, even if by indexing only part of the object is
> used.
> I noted that some attributes like levels and class of a factor exist also
> after indexing, while others, like comment or label vanish.
> Is there a way to make an arbitrary attribute to be kept after indexing?
> This would be especially useful when indexing a data.frame.
> 
> ## example for loss of attributes
> fx <- factor(1:5, ordered=TRUE)
> attr(fx, 'comment') <- 'Comment for fx'
> attr(fx, 'label') <- 'Label for fx'
> attr(fx, 'testattribute') <- 'just for fun'
> attributes(fx)          # all attributes are shown
> attributes(fx[])        # all attributes are shown
> attributes(fx[1:5])     # only levels and class are shown
> attributes(fx[1])       # only levels and class are shown
> 
> Thanks,
> 
> Heinz T?chler
"Non-standard" attributes do not survive the use of "[". You
could
create a new class and subset method for the objects where you require
this type of functionality.

Frank Harrell has done that in the Hmisc package to support the use of
the labeling attributes, which in turn are used by some of his functions
such as latex().  You might want to review what he has done in ?label
where the "[.labelled" method has been added.

Alternatively, you could create your own function to save the
attributes, do the subsetting and then restore the attributes to the
resultant object.

HTH,

Marc Schwartz

You could create your own child class with its own [ method.

"[.myfactor" <- function(x, ...) {
       attr <- attributes(x)
       x <- NextMethod("[")
       attributes(x) <- attr
       x
}

gx <- structure(fx, class = c("myfactor", class(fx)))
attributes(gx[1])


On 5/24/06, Heinz Tuechler <tuechler at gmx.at>
wrote:
> Dear All!
>
> For descriptive purposes I would like to add attributes to objects. These
> attributes should be kept, even if by indexing only part of the object is
> used.
> I noted that some attributes like levels and class of a factor exist also
> after indexing, while others, like comment or label vanish.
> Is there a way to make an arbitrary attribute to be kept after indexing?
> This would be especially useful when indexing a data.frame.
>
> ## example for loss of attributes
> fx <- factor(1:5, ordered=TRUE)
> attr(fx, 'comment') <- 'Comment for fx'
> attr(fx, 'label') <- 'Label for fx'
> attr(fx, 'testattribute') <- 'just for fun'
> attributes(fx)          # all attributes are shown
> attributes(fx[])        # all attributes are shown
> attributes(fx[1:5])     # only levels and class are shown
> attributes(fx[1])       # only levels and class are shown
>
> Thanks,
>
> Heinz T?chler
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide!
http://www.R-project.org/posting-guide.html
>

Dear All!

For descriptive purposes I would like to add attributes to objects. These
attributes should be kept, even if by indexing only part of the object is
used.
I noted that some attributes like levels and class of a factor exist also
after indexing, while others, like comment or label vanish.
Is there a way to make an arbitrary attribute to be kept after indexing?
This would be especially useful when indexing a data.frame.

## example for loss of attributes
fx <- factor(1:5, ordered=TRUE)
attr(fx, 'comment') <- 'Comment for fx'
attr(fx, 'label') <- 'Label for fx'
attr(fx, 'testattribute') <- 'just for fun'
attributes(fx)          # all attributes are shown
attributes(fx[])        # all attributes are shown
attributes(fx[1:5])     # only levels and class are shown
attributes(fx[1])       # only levels and class are shown

Thanks,

Heinz T?chler

Thank you for your answer, Gabor. I will see, if I understood it.

Heinz

At 11:31 24.05.2006 -0400, Gabor Grothendieck wrote:
>You could create your own child class with its own [ method.
>
>"[.myfactor" <- function(x, ...) {
>       attr <- attributes(x)
>       x <- NextMethod("[")
>       attributes(x) <- attr
>       x
>}
>
>gx <- structure(fx, class = c("myfactor", class(fx)))
>attributes(gx[1])
>
>
>On 5/24/06, Heinz Tuechler <tuechler at gmx.at> wrote:
>> Dear All!
>>
>> For descriptive purposes I would like to add attributes to objects.
These
>> attributes should be kept, even if by indexing only part of the object
is
>> used.
>> I noted that some attributes like levels and class of a factor exist
also
>> after indexing, while others, like comment or label vanish.
>> Is there a way to make an arbitrary attribute to be kept after
indexing?
>> This would be especially useful when indexing a data.frame.
>>
>> ## example for loss of attributes
>> fx <- factor(1:5, ordered=TRUE)
>> attr(fx, 'comment') <- 'Comment for fx'
>> attr(fx, 'label') <- 'Label for fx'
>> attr(fx, 'testattribute') <- 'just for fun'
>> attributes(fx)          # all attributes are shown
>> attributes(fx[])        # all attributes are shown
>> attributes(fx[1:5])     # only levels and class are shown
>> attributes(fx[1])       # only levels and class are shown
>>
>> Thanks,
>>
>> Heinz T?chler
>>
>> ______________________________________________
>> R-help at stat.math.ethz.ch mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide!
http://www.R-project.org/posting-guide.html
>>
>
>