R/StatEllipse.R

In low-decarie/ggpca: Creates ggplot biplot methods for pca objects

StatEllipse <- proto(ggplot2:::Stat,
{
  required_aes <- c("x", "y")
  default_geom <- function(.) GeomPath
  objname <- "ellipse"
  
  calculate_groups <- function(., data, scales, ...){
    .super$calculate_groups(., data, scales,...)
  }
  calculate <- function(., data, scales, level = 0.75, segments = 51,...){
    dfn <- 2
    dfd <- length(data$x) - 1
    if (dfd < 3){
      ellipse <- rbind(c(NA,NA))    
    } else {
      v <- cov.trob(cbind(data$x, data$y))
      shape <- v$cov
      center <- v$center
      radius <- sqrt(dfn * qf(level, dfn, dfd))
      angles <- (0:segments) * 2 * pi/segments
      unit.circle <- cbind(cos(angles), sin(angles))
      ellipse <- t(center + radius * t(unit.circle %*% chol(shape)))
    }
    
    ellipse <- as.data.frame(ellipse)
    colnames(ellipse) <- c("x","y")
    return(ellipse)
  }
}
)