Starting in SVN revision 47035 (which shows up in the R-2-9-0 line), transform.data.frame() started accepting arguments like 'row.names' and 'stringsAsFactors' to be passed through to the data.frame() function.  It looks like this was an unintentional side-effect of letting multiple columns be added properly.

Given that this has been implemented for quite a while, should it now be documented?  It's a little strange to support it though - the 'stringsAsFactors' argument might be handy, but 'check.names', 'row.names', and 'check.rows' are perhaps questionable.  If it's desirable to document the behavior, here's a possible patch.

---------------------------------------------
Index: src/library/base/man/transform.Rd
===================================================================
--- src/library/base/man/transform.Rd  (revision 61043)
+++ src/library/base/man/transform.Rd               (working copy)
@@ -27,6 +27,10 @@
   \code{_data}.  The tags are matched against \code{names(_data)}, and for
   those that match, the value replace the corresponding variable in
   \code{_data}, and the others are appended to \code{_data}.
+
+  \code{transform.data.frame} also accepts the additional named
+  arguments that the \code{data.frame} function accepts,
+  e.g. \code{stringsAsFactors}.
}
 \value{
   The modified value of \code{_data}.
---------------------------------------------

--
Ken Williams, Senior Research Scientist
WindLogics
http://windlogics.com


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