[Rd] computation with vectors of length 0 (PR#2716)
Prof Brian Ripley
ripley at stats.ox.ac.uk
Tue Apr 1 17:13:43 MEST 2003
Your report is `obviously misleading', as you seem unaware of the standard
mathematical definitions. You also seem unaware that R statements are
terminated by a newline, so you have a while series of empty statements
and should not have the semicolons.
The sum of an empty vector is 0, by definition.
The mean of an empty vector is 0/0 = NaN, by definition.
The variance and hence the standard deviation are undefined unless n >= 1.
None of them are missing, so it would be incorrect to return NA.
On Tue, 1 Apr 2003 klaus.hermann at metagen.de wrote:
> Full_Name: Klaus Hermann
> Version: 1.5.0
> OS: SUNRAY - Unix
> Submission from: (NULL) (220.127.116.11)
> if we produce a numeric vector of length 0 and want compute the sum over its
> the sum function returns 0 - this is obviously misleading. Better would be to
> NA and give a corresponding warning.
> There should be a unified strategy to handle vectors of length 0.
There is: to use the standard mathematical definitions. One could debate
what var(numeric(0)) should be, but we decided that was most consistently
> For example the functions sum, mean, sd handle such vectors in a different way
> classfreq <- c(3,3,3,3);
> classfreq <- classfreq[classfreq != 3];
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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