Good point. Perhaps what is needed is a Note clarifying all this in ?mean (unless the software itself is reworked as Martin has discussed).
Regarding var(x), one could use sd(x)^2. On 1/25/07, Berwin A Turlach <[EMAIL PROTECTED]> wrote: > G'day Gabor, > > On Thu, 25 Jan 2007 09:53:49 -0500 > "Gabor Grothendieck" <[EMAIL PROTECTED]> wrote: > > > The help page for mean does not say what happens when one > > applies mean to a matrix. > > Well, not directly. :-) > > But the help page of mean says that one of the arguments is: > > x: An R object. Currently there are methods for numeric data > frames, numeric vectors and dates. A complex vector is > allowed for 'trim = 0', only. > > And the `Value' section states: > > For a data frame, a named vector with the appropriate method being > applied column by column. > > If 'trim' is zero (the default), the arithmetic mean of the values > in 'x' is computed, as a numeric or complex vector of length one. > If any argument is not logical (coerced to numeric), integer, > numeric or complex, 'NA' is returned, with a warning. > > Since a matrix is a vector with a dimension attribute, and not a data > frame, one can deduce that the second paragraph describes the return > value for `mean(x)' when x is a matrix. > > As I always tell my students, reading R help pages is a bit of an > art. :) > > > mean and sd work in an inconsistent way on a matrix so that should at > > least be documented. > > Agreed. But it is documented in the help page of sd, which clearly > states: > > [....] If 'x' is a matrix or a data frame, a vector > of the standard deviation of the columns is returned. > > I guess you also want to have it documented in the mean help page? > > But then, should `var' also be mentioned in the mean help page? This > command also work in an a different and inconsistent manner to mean on > matrices. > > And, of course, there are other subtle inconsistencies in the language > used in these help pages. Note that the mean help page talks about > "numeric data frames" while the help pages of `var' and `se' talk about > "data frames" only, though all components of the data frame have to be > numeric, of course. > > > Also there should be a See Also to colMeans since that provides the > > missing column-wise analog to sd. > > That's probably a good idea. What would you suggest should be > mentioned to provide the column-wise analog of `var'? > > Cheers, > > Berwin > ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
