Yes, this behavior is new in 2.11.x. From the NEWS file:

o	write.csv[2] no longer allow 'append' to be changed: as ever,
	direct calls to write.table() give more flexibility as well as
	more room for error.

HTH,

Marc

On Jul 15, 2010, at 3:01 PM, Jonathan Christensen wrote:

> Out of curiosity, is this a change in 2.11? I'm still runnning 2.10.1, ?write.csv mentions the other options being ignored, but not append. This might also explain why John Kane believes he has successfully used append with write.csv in that past.
> 
> Jonathan
> 
> 
> On Thu, Jul 15, 2010 at 9:36 AM, Marc Schwartz <marc_schwartz@me.com> wrote:
> On Jul 15, 2010, at 9:41 AM, Cliff Clive wrote:
> 
> >
> > I'm running R 2.11.0 on a 32-bit Windows XP machine.  Whenever I try to write
> > a csv file with 'append' set to TRUE, I get this message: attempt to set
> > 'append' ignored.
> >
> > Obviously, this is no good, since R is deleting my previously saved data
> > files, rather than appending to them.  What can I do to fix this?
> 
> 
> Read ?write.csv more carefully:
> 
> In the "CSV files" section:
> 
> These wrappers are deliberately inflexible: they are designed to ensure that the correct conventions are used to write a valid file. Attempts to change append, col.names, sep, dec or qmethod are ignored, with a warning.
> 
> 
> If you want to use 'append', you will need to use write.table() and adjust the other arguments as you require.
> 
> HTH,
> 
> Marc Schwartz


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