Peng,
You can create all the attributes you want, with one headache: R does
not keep attributes across subsetting operations so you need to write
classes and "[.something" methods when attributions need to be kept or
adjusted upon subsetting rows.
The Hmisc package uses attributes such as label, units, imputed. You
might look at the code to see how it did that. For example, label(x)
will use attr(x, 'label') to fetch the 'label' attribute. There
are
attribute-setting functions there too.
Frank
Peng Yu wrote:> Hi,
>
> According to the example below this email, attr(x,"names") is the
same
> as names(x). I am wondering how many attributes there are of a given
> variable. How to find out what they are? Can I always use
> some_attribute(x) instead of attr(x, "some_attribute")?
>
> Regards,
> Peng
>
>> x=c(1,2,3)
>> attr(x,"names")=c("a","b","c")
>> x
> a b c
> 1 2 3
>> y=c(1,2,3)
>> names(y)=c("a","b","c")
>> y
> a b c
> 1 2 3
>
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--
Frank E Harrell Jr Professor and Chair School of Medicine
Department of Biostatistics Vanderbilt University