[R] tapply and empty subsets

Patrick Connolly p.connolly at hortresearch.co.nz
Wed May 15 04:23:04 CEST 2002

On Tue, 14-May-2002 at 11:13PM +0000, jasont at indigoindustrial.co.nz wrote:
|> > I guess for my purpose the following will do.
|> > 
|> > > x <- tapply(y, z, mean)
|> > > x[is.na(x)] <- 0
|> > 
|> > Thanks,
|> > Giovanni

|> If I might ask, what's wrong with NA?  I occasionally deal with
|> data sets that do have means close to zero, so my doing this would
|> be misleading at best (YMMV).  NA is a good thing, for me.

Well, I've had occasions where NA was really zero.  Depends on what
sort of data you have and who entered it in whatever form it was done.
A control reading that can be safely assumed to be zero is an example
that comes to mind.

|> If you just can't live with NA, na.omit(tapply(y,z,mean)) might be more 
|> appropriate here.

Think that will end up with only two, and we need to know which of the
three is missing (and isn't really NA).


Patrick Connolly
Mt Albert
New Zealand 
Ph: +64-9 815 4200 x 7188
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