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

On Fri, 24 Aug 2001 pauljohn at ukans.edu wrote:

I will try this method to export a sas file, but reading it made
me wonder about "variable lables" and "value lables" in R.  In
SAS and SPSS, the lables are a huge chunk of code and people
want to hang onto them.  In case you have not used data from the
Universty of Michigan's ICPSR, you might not have seen how
elaborate this can get.  Here's a link to a SAS program that
reads in an ascii dataset. It has thousands of lables:

http://lark.cc.ukans.edu/~pauljohn/sa2684.gz

(This is a famous one, the American National Election Study)

Netscape unzips this and shows it as text on the screen.

A program like SAS or SPSS will use these lables to beautify
frequencies and such, and I've not heard much in the R group
about it, and I just wondered if you do ever talk about it.

Because it's no big deal. Those are factor levels.  R has factors.
Whether they get exported from SAS and converted by read.xpt I can't say.

Preserving value labels from SAS datasets is not as easy as it should be.

SAS value labels are not part of the dataset, but are kept in a separate
file called a format catalogue. The XPORT engine does not work with SAS
catalogues, so you need to convert the format catalogue to a SAS database.
You can do this with the cntlout option in PROC FORMAT. [Conversely the
cntlin option creates a format catalogue from a database.]

We use a program called Stat/Transfer to convert between different
file formats.  Recent versions of Stat/Transfer will preserve SAS value
labels if you supply a format dataset.  [It  doesn't support R, but you
can get from SAS to R via Stata]. I suppose that you could get read.xport
to work the same way ...

SAS value labels are not quite the same as S factor labels since
the mapping from values to labels may be many-to-one.  For example, you
can categorize a continuous variable by supplying ranges of values to be
given the same label.  The variable is then treated like a categorical
variable in tabulations, etc. but the underlying values are preserved
in the dataset and may be recovered by changing the format.

Martyn
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