directlabels - utility.function - Positioning Method - gapply

apply a Positioning Method to every group. works like ddply from plyr package, but the grouping column is always called groups, and the Positioning Method is not necessarily a function (but can be).

gapply <- function
### apply a Positioning Method to every group. works like ddply from
### plyr package, but the grouping column is always called groups, and
### the Positioning Method is not necessarily a function (but can be).
(d,
### data frame with column groups.
 method,
### Positioning Method to apply to every group separately.
 ...,
### additional arguments, passed to Positioning Methods.
 groups="groups"
### can also be useful for piece column.
 ){
  stopifnot(is.data.frame(d))
  dfs <- split(d,as.character(d[[groups]]))
  f <- function(d,...){
    res <- apply.method(method,d,columns.to.check=c("x","y"),...)
    res[[groups]] <- d[[groups]][1]
    res
  }
  results <- lapply(dfs,f,...)
  if(any(!sapply(results,is.data.frame))){
    print(results)
    stop("Positioning Method did not return data.frame")
  }
  do.call(rbind,results)
### data frame of results after applying FUN to each group in d.
}