panel.ellipse {latticeExtra}

Lattice panel function to fit and draw a confidence ellipsoid from bivariate data.

Description

A lattice panel function that computes and draws a confidence ellipsoid from bivariate data, possibly grouped by a third variable.

Usage

panel.ellipse(x, y, groups = NULL,
              level = 0.68, segments = 50, robust = FALSE,
              center.pch = 3, center.cex = 2, ...,
              type, pch, cex)

Arguments

x, y

Numeric vectors of same length giving the bivariate data. Non-numeric variables will be coerced to be numeric.

groups

Optional grouping variable.

level

Confidence level for the ellipse.

segments

Number of segments used to approximate the ellipse.

robust

Logical indicating whether a robust method should be used. If TRUE, the confidence ellipse is based on a bivariate t-distribution using the cov.trob function in the MASS package.

center.pch

Plotting character for the center (fitted mean). If NULL, the center will not be shown on the plot.

center.cex

Character expansion (size) multipler for the symbol indicating the center.

...

Further arguments, typically graphical parameters. Passed on to panel.xyplot.

type, pch, cex

Parameters that are ignored; these are present only to make sure they are not inadvertently passed on to panel.xyplot.

Author(s)

Deepayan Sarkar, extending code contributed by Michael Friendly.

Examples

xyplot(Sepal.Length ~ Petal.Length, groups=Species,
       data = iris, scales = "free",
       par.settings = list(superpose.symbol = list(pch=c(15:17)),
                           superpose.line = list(lwd=2, lty=1:3)),
       panel = function(x, y, ...) {
           panel.xyplot(x, y, ...)
           panel.ellipse(x, y, ...)
       },
       auto.key = list(x = .1, y = .8, corner = c(0, 0)))

## Without groups
xyplot(Sepal.Length ~ Petal.Length, 
       data = iris, scales = "free",
       par.settings = list(plot.symbol = list(cex = 1.1, pch=16)),
       panel = function(x, y, ...) {
           panel.xyplot(x, y, ...)
           panel.ellipse(x, y, lwd = 2, ...)
       },
       auto.key = list(x = .1, y = .8, corner = c(0, 0)))


## With conditioning
xyplot(Sepal.Length ~ Petal.Length | Species, 
       data = iris, scales = "free",
       par.settings = list(plot.symbol = list(cex = 1.1, pch=16)),
       layout=c(2,2),
       panel = function(x, y, ...) {
           panel.xyplot(x, y, ...)
           panel.ellipse(x, y, lwd = 2, ...)
       },
       auto.key = list(x = .6, y = .8, corner = c(0, 0)))


## Compare classical with robust 
xyplot(Sepal.Length ~ Petal.Length | Species, 
       data = iris, scales = "free",
       par.settings = list(plot.symbol = list(cex = 1.1, pch=16)),
       layout=c(2,2),
       panel = function(x, y, ...) {
           panel.xyplot(x, y, ...)
           panel.ellipse(x, y, lwd = 2, ...)
           panel.ellipse(x, y, lwd = 2, col="red", robust=TRUE,  ...)
       })