directlabels - utility.function - Positioning Method - make.tiebreaker

Make a tiebreaker function that can be used with qp.labels.

make.tiebreaker <- function(x.var,tiebreak.var){
  force(x.var)
  force(tiebreak.var)
  function(d,...){
    orig <- attr(d,"orig.data")
    xvals <- unique(orig[,x.var])
    x <- unique(d[,x.var])
    if(length(x)>1){
      stop("labels are not aligned")
    }
    xvals <- xvals[order(abs(xvals-x))]
    group.dfs <- split(orig,orig$groups)
    m <- do.call(cbind,lapply(d$groups,function(g){
      df <- group.dfs[[as.character(g)]]
      approx(df[,x.var],df[,tiebreak.var],xvals)$y
    }))
    ## useful for debugging:
    ##print(m)
    L <- lapply(1:nrow(m),function(i)m[i,])
    do.call(order,L)
  }
}