PositionHeap for ggplot2

PositionHeap.R

library(ggplot2)

df <- data.frame(a=sample(1:500,1000,replace=T),b=1)


PositionHeap <- proto(Position, {
  adjust <- function(., data, scales) {
    if (empty(data)) return(data.frame())
    check_required_aesthetics(c("x", "y"), names(data), "position_stacking")

    if (is.null(.$height)) .$height <- resolution(data$x) * 0.4
    if (is.null(.$width)) .$width <- resolution(data$y) * 0.4

    data$offset.y <- 0
    data$offset.x <- 0

    dups <- (1:nrow(data))[duplicated(data)]
    cat(system.time(for (i in dups) {
      ddups <- (data$x==data$x[i]) & (data$y==data$y[i])
      ddups[1:i] <- FALSE
      data$offset.y[ddups] <- data$offset.y[ddups]+.$height
      data$offset.x[ddups] <- data$offset.x[ddups]+.$width
    }))
    
    
    data$y <- data$y+data$offset.y
    data$x <- data$x+data$offset.x
    return(data)
  }
  objname <- "stacking" 
  desc <- "stacking points to avoid overplotting"
  
  examples <- function(.) {
    qplot(am, vs, data=mtcars)
    
    # Default amount of jittering will generally be too much for 
    # small datasets:
    qplot(am, vs, data=mtcars, position="stacking")
    # Control the amount as follows
    qplot(am, vs, data=mtcars, position=position_stacking(w=0.0, h=0.1))
    qplot(am, vs, data=mtcars, position=position_stacking(w=0.1, h=0.0))
  }
})

position_stacking <- PositionHeap$build_accessor()

ggplot(df,aes(x=a,y=b,)) + geom_point(,position=position_stacking(w=0.0,h=1))