Author: David Zelený

Function which adds group centroids onto ordination diagram. The code heavily borrows from the vegan function ordispider, written by Jari Oksanen. Use of ordicenter (including the names of its arguments) has the same logic (for details about the arguments and use, consult help to ordispider function).

See here for examples how to use this function.

ordicenter.r

ordicenter <- function (ord, groups, display = "sites", w = weights(ord, display), 
            show.groups, ...) 
  {
    weights.default <- function(object, ...) NULL
    pts <- scores(ord, display = display, ...)
    w <- eval(w)
    if (length(w) == 1) 
      w <- rep(1, nrow(pts))
    if (is.null(w)) 
      w <- rep(1, nrow(pts))
    if (!missing(show.groups)) 
    {
      take <- groups %in% show.groups
      pts <- pts[take, , drop = FALSE]
      groups <- groups[take]
      w <- w[take]
    }
    out <- seq(along = groups)
    inds <- names(table(groups))
    for (is in inds) 
    {
      gr <- out[groups == is]
      if (length(gr) > 1)
      {
        X <- pts[gr, ]
        W <- w[gr]
        ave <- apply(X, 2, weighted.mean, w = W)
        vegan:::ordiArgAbsorber(ave[1], ave[2], labels = is, FUN = text, ...)
      }
      if (length(gr) == 1)
      {
        X <- pts[gr, ]
        W <- w[gr]
        vegan:::ordiArgAbsorber(X[1], X[2], labels = is, FUN = text, ...)
      }
    }
    invisible()
  }