[R] How many attributes are there of a variable?

[Frank E Harrell Jr]

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