[Rd] Re: Variable labels (was Re: [R] Reading SAS version 8 data into

[fharrell@virginia.edu]

"Warnes, Gregory R" wrote:
> 
> > From: fharrell@virginia.edu [mailto:fharrell@virginia.edu]
> >
> [snip]
> > I think your code is more complex that is really needed.
> >
> > The problem with defaulting to deparse(...) is that
> > multiple function pass-throughs return the wrong result:
> >
> [snip]
> > So I don't see a large role for the deparse(...) method.
> >
> 
> Actually one of the reasons that I included the deparse(...) method was to
> create a 'drop-in' substitute for the current calls to deparse(...) that are
> found throughout the code and that would be backward-compatible.  Having
> such a call will immensely simplify changing existing code.

Thanks for your reply Greg.
The "complex" code I was referring to was the eval()
and as.name() parts of your code.  The deparse can be
handy although I have done that on a case-by-case basis.
For example in a high-level plotting function I'll retrieve
label(an argument) and if that is empty I'll use
deparse(substitute(argument)).  
> 
> It's true that the variable names don't get correctly handled once you down
> a layer of function calls, but that applies AFAIK to the current
> deparse(...) method  as well.

Right.  That's why I try to define labels early when a data
frame is being created (e.g, in sas.get).

> 
> >
> > The Hmisc library already defines label<- so if you
> > are willing to use another name for your version that
> > would prevent confusion from users of Hmisc.
> 
> I don't think there will be a problem as long as the functions do exactly
> the same thing.  To that end, perhaps we should agree on a common set of
> functions and keep them in sync.  I expect that your functions are better
> tested than mine, since they've been available for some time.

Mine are simple:

label <- function(x)  {
	lab<-attr(x, "label")
	if(is.null(lab))lab<-""
	lab
	}

#From Bill Dunlap, StatSci  15Mar95:

"label<-" <- if(!.SV4.) function(x, value)
  structure(x, label=value,
            class=c('labelled',
              attr(x,'class')[attr(x,'class')!='labelled'])) else
function(x, value) {    # 1Nov00 for Splus 5.x, 6.x
  attr(x,'label') <- value
  x
}

For non SV4 systems (which include R) you see above that
when putting a label on a variable a class "labelled" is
added.  This is really to handle the subsetting problem
but I would rather get rid of it if subsetting can
respect selected attributes.

> 
> >
> > The problem of labels being retained after you do
> > arithmetic on the variable is a real one, and one
> > I've put up with for a long time with S-Plus.  It would
> > be nice if R could prevent that but that is getting tricky.
> 
> > What I've wanted more generally is the ability for the
> > user to specify a vector of attribute names in options()
> > that would be preserved upon subsetting.  That way I
> > wouldn't have to go to trouble to write local versions
> > of [.factor, etc. that carry the 'label' attribute.
> > Im my usage, 'label's are always logically carried
> > forward for subsetting.
> 
> It seems to be a good idea to preserve the labels during subset operations.
> What are the possible cons?

If the user or a package specifies the list of attribute names
to preserve (I can only think of 'label' and 'units' right now)
I don't see a downside.  -Frank

> 
> -Greg
> 
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-- 
Frank E Harrell Jr              Prof. of Biostatistics & Statistics
Div. of Biostatistics & Epidem. Dept. of Health Evaluation Sciences
U. Virginia School of Medicine  http://hesweb1.med.virginia.edu/biostat
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