#' Biplot method
#' 
#' Provides robust compositional biplots.
#' 
#' The robust compositional biplot according to Aitchison and Greenacre (2002),
#' computed from resulting (robust) loadings and scores, is performed.
#' 
#' @param x object of class \sQuote{factanal}
#' @param \dots ...
#' @return The robust compositional biplot.
#' @author M. Templ, K. Hron
#' @seealso \code{\link{pfa}}
#' @references Aitchison, J. and Greenacre, M. (2002). Biplots of compositional
#' data. \emph{Applied Statistics}, \bold{51}, 375-392. \
#' 
#' Filzmoser, P., Hron, K., Reimann, C. (2009) Principal Component Analysis for
#' Compositional Data with Outliers. \emph{Environmetrics}, \bold{20} (6),
#' 621--632.
#' @keywords aplot
#' @export
#' @method biplot factanal
#' @examples
#' 
#' data(expenditures)
#' p1 <- pcaCoDa(expenditures)
#' p1
#' biplot(p1)
#' 
#' 
#' ## with labels for the scores:
#' data(arcticLake)
#' rownames(arcticLake) <- paste(sample(letters[1:26],nrow(arcticLake), replace=TRUE), 
#'                               1:nrow(arcticLake), sep="")
#' pc <- pcaCoDa(arcticLake, method="standard")
#' plot(pc, xlabs=rownames(arcticLake))
#' 
#' 
biplot.factanal <- function(x, ...){
  if(is.null(x$scores)) warning("no scores computed")
  beschx <- if(x$robust) "Factor1 (clr-robust)" else "Factor1 (clr-classical)"
  beschy <- if(x$robust) "Factor2 (clr-robust)" else "Factor2 (clr-classical)"
  biplot(x$scores, x$loadings, xlab=beschx, ylab=beschy, ...)
}