meaning of "trim" in mean()
There is only one _range_ mentioned, (0, 0.5). I don't see how you can construe 'that range' to be a reference to anything other than (0, 0.5). And why do you suppose the description for argument 'trim' is referring to 'values' of a different argument? It is telling you what happens for values of trim < 0 or > 0.5: that is not information that it is appropriate to excise.
On Thu, 25 Oct 2007, Peter Dalgaard wrote:
Liaw, Andy wrote:
(I see this in both R-patched r43124 and R-devel r43233.) In the Argument section of ?mean: trim the fraction (0 to 0.5) of observations to be trimmed from each end of x before the mean is computed. Values outside that range are taken as the nearest endpoint. Then in the Value section: If trim is non-zero, a symmetrically trimmed mean is computed with a fraction of trim observations deleted from each end before the mean is computed. The description in "trim" to me sounds like Windsorizing, rather than trimming. Should that be edited?
I think so:
x <- sort(rnorm(10)) mean(x,trim=.1)
[1] -0.6387413
mean(x[2:9])
[1] -0.6387413
mean(x[c(2,2:9,9)]) # Winsorizing
[1] -0.6204222 So yes, it is trimming, not Winsorizing, and the last sentence in the description of "trim" is misleading and should be, well..., trimmed.
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