Description Usage Arguments Details Value Author(s) See Also Examples
The function draws covariance ellipses for one or more groups
and optionally for the pooled total sample. It
uses either the classical productmoment covariance estimate, or a
robust alternative, as provided by cov.rob
.
Provisions are provided to do this for more than two variables,
in a scatterplot matrix format.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26  covEllipses(x, ...)
## S3 method for class 'boxM'
covEllipses(x, ...)
## S3 method for class 'data.frame'
covEllipses(x, group, pooled = TRUE, method = c("classical", "mve", "mcd"), ...)
## S3 method for class 'matrix'
covEllipses(x, group, pooled = TRUE, method = c("classical", "mve", "mcd"), ...)
## Default S3 method:
covEllipses(x, means, df,
labels = NULL, variables = 1:2, level = 0.68,
segments = 60,
center = FALSE, center.pch = "+", center.cex = 2,
col = getOption("heplot.colors", c("red", "blue", "black", "darkgreen",
"darkcyan", "brown", "magenta", "darkgray")),
lty = 1, lwd = 2,
fill = FALSE, fill.alpha = 0.3,
label.pos = 0,
xlab, ylab,
vlabels, var.cex=2,
main = "",
xlim, ylim, axes = TRUE,
offset.axes, add = FALSE, ...)

x 
The generic argument. For the default method, this is a list of covariance matrices.
For the 
group 
a factor defining groups, or a vector of length 
pooled 
Logical; if 
method 
the covariance method to be used: classical productmoment ( 
means 
For the default method, a matrix of the means for all groups (followed by the grand means, if 
df 
For the default method, a vector of the degrees of freedom for the covariance matrices 
labels 
Either a character vector of labels for the groups, or 
variables 
indices or names of the response variables to be plotted;
defaults to 
level 
equivalent coverage of a data ellipse for normallydistributed
errors, defaults to 
segments 
number of line segments composing each ellipse; defaults to

center 
If 
center.pch 
character to use in plotting the centroid of the data;
defaults to 
center.cex 
size of character to use in plotting the centroid of the data;
defaults to 
col 
a color or vector of colors to use in plotting ellipses
— recycled as necessary
A single color can be given, in which case it is used for all ellipses.
For convenience, the default colors for all plots produced in a given session can be changed
by assigning a color vector via 
lty 
vector of line types to use for plotting the ellipses; the first is
used for the error ellipse, the rest — possibly recycled — for
the hypothesis ellipses; a single line type can be given. Defaults to

lwd 
vector of line widths to use for plotting the ellipses; the first is
used for the error ellipse, the rest — possibly recycled — for
the hypothesis ellipses; a single line width can be given. Defaults to

fill 
A logical vector indicating whether each ellipse should be filled or not. The first value is used for the error ellipse, the rest — possibly recycled — for the hypothesis ellipses; a single fill value can be given. Defaults to FALSE for backward compatibility. See Details below. 
fill.alpha 
Alpha transparency for filled ellipses, a numeric scalar or vector of values
within 
label.pos 
Label position, a vector of integers (in 
xlab 
xaxis label; defaults to name of the x variable. 
ylab 
yaxis label; defaults to name of the y variable. 
vlabels 
Labels for the variables can also be supplied through this argument, which is more convenient
when 
var.cex 
character size for variable labels in the pairs plot 
main 
main plot label; defaults to 
xlim 
xaxis limits; if absent, will be computed from the data. 
ylim 
yaxis limits; if absent, will be computed from the data. 
axes 
Whether to draw the x, y axes; defaults to 
offset.axes 
proportion to extend the axes in each direction if computed from the data; optional. 
add 
if 
... 
Other arguments passed to the default method for 
These plot methods provide one way to visualize possible heterogeneity of withingroup covariance matrices in a oneway MANOVA design. When covariance matrices are nearly equal, their covariance ellipses should all have the same shape. When centered at a common mean, they should also all overlap.
The can also be used to visualize the difference between classical and robust covariance matrices.
Nothing is returned. The function is used for its sideeffect of producing a plot.
Michael Friendly
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23  data(iris)
# compare classical and robust covariance estimates
covEllipses(iris[,1:4], iris$Species)
covEllipses(iris[,1:4], iris$Species, fill=TRUE, method="mve", add=TRUE, labels="")
# method for a boxM object
x < boxM(iris[, 1:4], iris[, "Species"])
x
covEllipses(x, fill=c(rep(FALSE,3), TRUE) )
covEllipses(x, fill=c(rep(FALSE,3), TRUE), center=TRUE, label.pos=1:4 )
# method for a list of covariance matrices
cov < c(x$cov, pooled=list(x$pooled))
df < c(table(iris$Species)1, nrow(iris)3)
covEllipses(cov, x$means, df, label.pos=3, fill=c(rep(FALSE,3), TRUE))
covEllipses(cov, x$means, df, label.pos=3, fill=c(rep(FALSE,3), TRUE), center=TRUE)
# scatterplot matrix version
covEllipses(iris[,1:4], iris$Species,
fill=c(rep(FALSE,3), TRUE), variables=1:4,
fill.alpha=.1)

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