CovSde | R Documentation |
Compute a robust estimate of location and scale using the Stahel-Donoho projection based estimator
CovSde(x, nsamp, maxres, tune = 0.95, eps = 0.5, prob = 0.99,
seed = NULL, trace = FALSE, control)
x |
a matrix or data frame. |
nsamp |
a positive integer giving the number of resamples required;
|
maxres |
a positive integer specifying the maximum number of
resamples to be performed including those that are discarded due to linearly
dependent subsamples. If |
tune |
a numeric value between 0 and 1 giving the fraction of the data to receive non-zero weight.
Defaults to |
prob |
a numeric value between 0 and 1 specifying the probability of high breakdown point;
used to compute |
eps |
a numeric value between 0 and 0.5 specifying the breakdown point; used to compute
|
seed |
starting value for random generator. Default is |
trace |
whether to print intermediate results. Default is |
control |
a control object (S4) of class |
The projection based Stahel-Donoho estimator posses very good statistical properties,
but it can be very slow if the number of variables is too large. It is recommended to use
this estimator if n <= 1000
and p<=10
or n <= 5000
and p<=5
.
The number of subsamples required is calculated to provide a breakdown point of
eps
with probability prob
and can reach values larger than
the larger integer value - in such case it is limited to .Machine$integer.max
.
Of course you could provide nsamp
in the call, i.e. nsamp=1000
but
this will not guarantee the required breakdown point of th eestimator.
For larger data sets it is better to use CovMcd
or CovOgk
.
If you use CovRobust
, the estimator will be selected automatically
according on the size of the data set.
An S4 object of class CovSde-class
which is a subclass of the
virtual class CovRobust-class
.
The Fortran code for the Stahel-Donoho method was taken almost with no changes from
package robust
which in turn has it from the Insightful Robust Library
(thanks to by Kjell Konis).
Valentin Todorov valentin.todorov@chello.at and Kjell Konis kjell.konis@epfl.ch
R. A. Maronna and V.J. Yohai (1995) The Behavior of the Stahel-Donoho Robust Multivariate Estimator. Journal of the American Statistical Association 90 (429), 330–341.
R. A. Maronna, D. Martin and V. Yohai (2006). Robust Statistics: Theory and Methods. Wiley, New York.
Todorov V & Filzmoser P (2009), An Object Oriented Framework for Robust Multivariate Analysis. Journal of Statistical Software, 32(3), 1–47. \Sexpr[results=rd]{tools:::Rd_expr_doi("10.18637/jss.v032.i03")}.
data(hbk)
hbk.x <- data.matrix(hbk[, 1:3])
CovSde(hbk.x)
## the following four statements are equivalent
c0 <- CovSde(hbk.x)
c1 <- CovSde(hbk.x, nsamp=2000)
c2 <- CovSde(hbk.x, control = CovControlSde(nsamp=2000))
c3 <- CovSde(hbk.x, control = new("CovControlSde", nsamp=2000))
## direct specification overrides control one:
c4 <- CovSde(hbk.x, nsamp=100,
control = CovControlSde(nsamp=2000))
c1
summary(c1)
plot(c1)
## Use the function CovRobust() - if no estimation method is
## specified, for small data sets CovSde() will be called
cr <- CovRobust(hbk.x)
cr
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