[R] variable labels to accompany data.frame

[Ista Zahn]

Alzola and Harrell discuss some of these issues in "An introduction to
S and the Hmisc and Design Libraries".

-ista

On Wed, Oct 28, 2009 at 1:27 PM, Jacob Wegelin <jacobwegelin at fastmail.fm> wrote:
>
> Often it is useful to keep a "codebook" to document the contents of a
> dataset. (By "dataset" I mean
> a rectangular structure such as a dataframe.)
>
> The codebook has as many rows as the dataset has columns (variables,
> fields).  The columns (fields)
> of the codebook may include:
>
>        •       variable name
>
>        •       type (character, factor, integer, etc)
>
>        •       variable label (e.g., a variable called "bmi2" might be
> labeled "BMI hand-input by
>        clinic personnel, must be checked"
>
>        •       permissible values
>
>        •       which values indicate missing (and potentially different
> kinds of missing)
>
> Some statistics software (e.g., SPSS and Stata) provides at least a subset
> of this kind of
> information automatically in a convenient form. For instance, in Stata one
> can define a "label" for
> a variable and it is thenceforth linked to the variable. In output from
> certain modeling and
> graphics functions, Stata by default uses the label rather than the variable
> name.
>
> Furthemore: In Stata, if "myvariable" is labeled numeric (in R lingo, a
> factor), and I type
>
> codebook myvariable
>
> then Stata tells me, among other things, the "levels" of myvariable.
>
> Does a tool of this sort exist in R?
>
> The prompt() function is related to this, but prompt(someDataFrame) creates
> a text file on disk. The
> text file is associated with, but not unambiguously linked to,
> someDataFrame.
>
> The epicalc function codebook() provides a summary of a dataframe similar to
> that created by
> summary() but easier to read. But this is not a way to define and keep track
> of labels that are
> linked to variables.
>
> To link a dataframe to its codebook, one could do the following "by hand":
> Create a list, say,
> "somedata", where somedata$DATA is a dataframe that contains the data, and
> somedata$VARIABLE is also
> a dataframe, but serves as the codebook. For instance, the following
> function creates a template
> into which one could subsequently edit to insert variable labels and turn
> into somedata$VARIABLE.
>
> fnJunk <-function( THESEDATA ) {
> #  From a dataframe, make the start of a codebook.
>   if(!is.data.frame(THESEDATA)) stop("!is.data.frame(THESEDATA)")
>   data.frame(
>      Variable=names(THESEDATA)
>      , class=sapply(THESEDATA, class)
>      , type=sapply(THESEDATA, typeof)
>      , label=""
>      , comment=""
>      )
> }
>
>
> But the following automatic behavior would be nice:
>
>        •       We should be able to treat somedata exactly as we treat a
> dataframe, so that the
>        fact that it possesses a "codebook" is merely an added benefit, not
> an interference with the
>        usual tasks.
>
>        •       If we delete a column of somedata$DATA, the associated row of
> somedata$VARIABLE
>        should be automatically deleted.
>
>        •       If we add a column to somedata$DATA, the associated column
> should be inserted in
>        somedata$VARIABLE, and some of the fields automatically populated
> such as variable name and
>        type.  It could get fancier. For instance:
>
>        •       If we try to add a value to a field in somedata$DATA which is
> not permitted by the
>        "permissible values" listed for this field in somedata$VARIABLE, we
> get an error.
>
> Has anyone already thought this through, maybe defined a class and
> associated methods?
>
> Thanks
>
> Jacob A. Wegelin
> Assistant Professor
> Department of Biostatistics
> Virginia Commonwealth University
> 730 East Broad Street Room 3006
> P. O. Box 980032
> Richmond VA 23298-0032
> U.S.A. E-mail: jwegelin at vcu.edu URL: http://www.people.vcu.edu/~jwegelin
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> and provide commented, minimal, self-contained, reproducible code.
>
>



-- 
Ista Zahn
Graduate student
University of Rochester
Department of Clinical and Social Psychology
http://yourpsyche.org