Peng, based on a suggestion, Frank made years ago (18.7.2006), I use
one attribute that contains all further attributes, I want to assign
to variables. It's necessary to create your own class and subsetting
method, so that this attribute does not get lost. Together with some
functions I use labels for variables, value.labels, missing.value
definitions etc.
It seems, without protection by your own class and the corresponding
subsetting method, you can never be sure, if an attribute survives subsetting.
Heinz
At 23:21 06.09.2009, Frank E Harrell Jr wrote:
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
______________________________________________
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and provide commented, minimal, self-contained, reproducible code.
______________________________________________
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
