On Aug 19, 2009, at 2:22 PM, Juliane Struve wrote:
Dear list,
the trim argument in mean(x,trim=0.1) can be used to exclude a
fraction of the observations when calculating the mean. There does
not seem to be a trim argument for sd(), is there some other way of
excluding observations when calculating the standard deviation ?
You could copy the methods used in mean. getAnywhere(mean.default)
exposes the preprocessing that is done before the vector is submitted
to .Internal(mean(x))
if (trim > 0 && n) {
if (is.complex(x))
stop("trimmed means are not defined for complex data")
if (trim >= 0.5)
return(stats::median(x, na.rm = FALSE))
lo <- floor(n * trim) + 1
hi <- n + 1 - lo
x <- sort.int(x, partial = unique(c(lo, hi)))[lo:hi]
--
David Winsemius, MD
Heritage Laboratories
West Hartford, CT
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