Re: [Rd] Inconsistency between rowMeans documentation and reality?

From: Gavin Simpson <gavin.simpson_at_ucl.ac.uk>
Date: Mon, 11 Apr 2011 16:11:29 +0100

On Mon, 2011-04-11 at 15:57 +0100, Prof Brian Ripley wrote:
> I suspect you omitted some of the help page:

Yes. My apologies, I don't know how I missed that - I did read it several times aware that I might be overlooking something sensible such as the sentence you quote.

Sorry for the noise.

G

> As they are written for speed, they blur over some of the subtleties
> of ‘NaN’ and ‘NA’.
>
> So, given that (and that real NA is a specific NaN) I think it is
> perfectly reasonable to claim they are consistent with mean.
>
> On Tue, 5 Apr 2011, Gavin Simpson wrote:
>
> > Dear List,
> >
> > I'm not even sure this is an issue or not, but ?rowMeans has:
> >
> > Value:
> >
> > A numeric or complex array of suitable size, or a vector if the
> > result is one-dimensional. The ‘dimnames’ (or ‘names’ for a
> > vector result) are taken from the original array.
> >
> > If there are no values in a range to be summed over (after
> > removing missing values with ‘na.rm = TRUE’), that component of
> > the output is set to ‘0’ (‘*Sums’) or ‘NA’ (‘*Means’), consistent
> > with ‘sum’ and ‘mean’.
> >
> > However the output of mean() and rowMeans() is not exactly the same when
> > all supplied values are missing.
> >
> >> mean(NA, na.rm = TRUE)
> > [1] NaN
> >> mean(rep(NA, 5), na.rm = TRUE)
> > [1] NaN
> >> rowMeans(matrix(rep(NA, 5), ncol = 5), na.rm = TRUE)
> > [1] NA
> >
> > So in one sense, the outputs are not consistent:
> >
> >> is.nan(mean(rep(NA, 5), na.rm = TRUE))
> > [1] TRUE
> >> is.nan(rowMeans(matrix(rep(NA, 5), ncol = 5), na.rm = TRUE))
> > [1] FALSE
> >
> > but in another they are:
> >
> >> is.na(mean(rep(NA, 5), na.rm = TRUE))
> > [1] TRUE
> >> is.na(rowMeans(matrix(rep(NA, 5), ncol = 5), na.rm = TRUE))
> > [1] TRUE
> >
> > I'm not familiar enough with the details to know if this even matters,
> > but wonder if something in the documentation needs a change or tweak to
> > clarify what is returned. As I say, in one sense the outputs are not
> > consistent.
> >
> >> sessionInfo()
> > R version 2.13.0 beta (2011-04-04 r55298)
> > Platform: x86_64-unknown-linux-gnu (64-bit)
> >
> > locale:
> > [1] LC_CTYPE=en_GB.utf8 LC_NUMERIC=C
> > [3] LC_TIME=en_GB.utf8 LC_COLLATE=en_GB.utf8
> > [5] LC_MONETARY=C LC_MESSAGES=en_GB.utf8
> > [7] LC_PAPER=en_GB.utf8 LC_NAME=C
> > [9] LC_ADDRESS=C LC_TELEPHONE=C
> > [11] LC_MEASUREMENT=en_GB.utf8 LC_IDENTIFICATION=C
> >
> > attached base packages:
> > [1] stats graphics grDevices utils datasets methods
> > [7] base
> >
> > loaded via a namespace (and not attached):
> > [1] tools_2.13.0
> >
> > Thanks,
> >
> > Gavin
> > --
> > %~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%
> > Dr. Gavin Simpson [t] +44 (0)20 7679 0522
> > ECRC, UCL Geography, [f] +44 (0)20 7679 0565
> > Pearson Building, [e] gavin.simpsonATNOSPAMucl.ac.uk
> > Gower Street, London [w] http://www.ucl.ac.uk/~ucfagls/
> > UK. WC1E 6BT. [w] http://www.freshwaters.org.uk
> > %~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%
> >
> > ______________________________________________
> > R-devel_at_r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-devel
> >
>
> --
> Brian D. Ripley, ripley_at_stats.ox.ac.uk
> 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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 Dr. Gavin Simpson             [t] +44 (0)20 7679 0522
 ECRC, UCL Geography,          [f] +44 (0)20 7679 0565
 Pearson Building,             [e] gavin.simpsonATNOSPAMucl.ac.uk
 Gower Street, London          [w] http://www.ucl.ac.uk/~ucfagls/
 UK. WC1E 6BT.                 [w] http://www.freshwaters.org.uk
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