R/gpanel_ellipse.R

In gmonette/spida15: Collection of miscellaneous functions for mixed models etc. prepared for SPIDA 2009+ (development version)

#' Lattice panel function for data ellipse
#' 
#' Draws a data ellipse in panels
#' 
#' 
#' @param x
#' @param y
#' @param ...
#' @return called for its side effects of plotting
#' @examples
#' 
#' \dontrun{
#' library(spida)
#' library(lattice)
#' library(latticeExtra)
#' # No groups or panels:
#' xyplot(mathach ~ ses, hs) + layer(gpanel.ellipse(...))
#' # Panels:
#' xyplot(mathach ~ ses | school, hs) + layer(gpanel.ellipse(...))
#' # Groups:
#' xyplot(mathach ~ ses, hs, groups = Sex) + glayer(gpanel.ellipse(...))
#' # Panels with groups:
#' xyplot(mathach ~ ses | school, hs, groups = Sex) + glayer(gpanel.ellipse(...))
#' }
#' 
#' @export
gpanel.ellipse <-
function(x, y, ..., radius = 1, n = 100, type) {
  mat <- na.omit(cbind(x,y))
  if( nrow(mat) < 3) return(NULL)
  ell <- do.call(dell,list(mat, radius = radius, n = n))
  panel.xyplot(ell[,1], ell[,2], ..., type = 'l')
}