There is no example to reproduce here. Please do show the courtesy to
follow the request at the bottom of every R-help posting and many other
places and provide some reproducible evidence to support your points.
On Wed, 21 Mar 2007, [EMAIL PROTECTED] wrote:
> Full_Name: Lutz Prechelt
> Version: 2.4.1
> OS: Windows XP
> Submission from: (NULL) (160.45.111.67)
>
>
> I stack a number of data.frames using rbind.
> Each of these dataframes has a column 'authorname', which is a factor
> and a column author = unclass(authorname) as piecewise pseudonyms.
> When using rbind to stack these dataframes, R warns about invalid factor
> levels
> and inserts all NAs in the author column.
>
> The reason appears to be that rbind.data.frame looks for the presence of
> levels,
> not actually for class==factor when deciding what to handle as a factor:
> if (!is.null(levels(xj))) {
>
> I find this behavior surprising, hence dangerous, and it is not documented.
> Rather, the documentation says:
> "The 'rbind' data frame method takes the classes of the columns
> from the first data frame, and matches columns by name (rather
> than by position). Factors have their levels expanded as
> necessary [...]"
>
> The behavior has bitten me fairly hard, because I searched for the origin of
> the
> warning in all the wrong places before finding the real one after about 3
> hours.
> (Although I still have not understood _why_ it results in that warning.)
>
> I believe the behavior of rbind.data.frame should be fixed, so that it ignores
> levels attributes when there is no factor class as well.
>
> The alternative would be to just add a warning to the documentation that
> 'unclass' on factors is insufficient if users want to avoid factor handling
> for
> rbind.
>
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> https://stat.ethz.ch/mailman/listinfo/r-devel
>
--
Brian D. Ripley, [EMAIL PROTECTED]
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272866 (PA)
Oxford OX1 3TG, UK Fax: +44 1865 272595
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