[R] Computing the mode
Thomas Petzoldt
thpe at hhbio.wasser.tu-dresden.de
Tue Feb 24 14:34:44 CET 2004
Aurora Torrente wrote:
> Hi all,
> I think this question could be quite trivial, but I can´t find out the
> solution... How can you compute the statistic "mode" of a sample, in
> case it exists (as mode() returns the mode of an object)? I tried
> help.search("mode") but I couldn't find a clue...
> Any help would be much appreciated. Regards,
There are several possibilities, e.g for *discrete* data:
x <- floor(runif(100, min=10, max=20)) # some discrete data
Half a year ago it was proposed to use e.g.:
x[rev(order(table(x)))[1]]
another possibility is:
f <- table(x)
as.numeric(names(f[max(f)==f])) # extracts mode(s) from vector names
For *continuous data* you can use class frequencies (from hist) together
with an interpolation formula. Another approximative solution uses
kernel density estimates (the density function):
x <- rnorm(100, mean=5, sd=1) # generate some data
hist(x, prob=TRUE)
dens <- density(x)
lines(dens)
dens$x[dens$y == max(dens$y)] # gives the mode
The precision depends on the parameters of the density() function. If
the distribution is multi-modal, I use a small function peaks() to
extract several maxima (a generalized version of the one in R-news
2003/3 p. 9).
Thomas P.
--
Thomas Petzoldt
Dresden University of Technology
Institute of Hydrobiology petzoldt at rcs.urz.tu-dresden.de
01062 Dresden http://www.tu-dresden.de/fghhihb/
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