How to use an image as a point in ggplot?

Question

Is there some way to use a specific small image as a point in a scatterplot with ggplot2. Ideally I will want to resize the images based on an variable.

Here's an example:

library(ggplot2) p <- ggplot(mtcars, aes(wt, mpg)) p + geom_point(aes(size = qsec, shape = factor(cyl))) 

So I basically want to know if there is a way to supply a specific image as the shape?

Answer 1

Here's a minimalist geom to display raster images instead of points,

library(ggplot2) library(grid)  ## replace by a named list with matrices to be displayed ## by rasterGrob .flaglist <- list("ar" = matrix(c("blue", "white", "blue"), 1),                    "fr" = matrix(c("blue", "white", "red"), 1))  flagGrob <- function(x, y, country, size=1, alpha=1){   grob(x=x, y=y, country=country, size=size, cl = "flag") }  drawDetails.flag <- function(x, recording=FALSE){    for(ii in seq_along(x$country)){     grid.raster(x$x[ii], x$y[ii],                  width = x$size[ii]*unit(1,"mm"), height = x$size[ii]*unit(0.5,"mm"),                 image = .flaglist[[x$country[[ii]]]], interpolate=FALSE)   } }   scale_country <- function(..., guide = "legend") {   sc <- discrete_scale("country", "identity", scales::identity_pal(), ..., guide = guide)    sc$super <- ScaleDiscreteIdentity   class(sc) <- class(ScaleDiscreteIdentity)   sc }  GeomFlag <- ggproto("GeomFlag", Geom,                     required_aes = c("x", "y", "country"),                     default_aes = aes(size = 5, country="fr"),                      draw_key = function (data, params, size)                      {                       flagGrob(0.5,0.5, country=data$country,  size=data$size)                     },                      draw_group = function(data, panel_scales, coord) {                       coords <- coord$transform(data, panel_scales)                            flagGrob(coords$x, coords$y, coords$country, coords$size)                     } )  geom_flag <- function(mapping = NULL, data = NULL, stat = "identity",                       position = "identity", na.rm = FALSE, show.legend = NA,                        inherit.aes = TRUE, ...) {   layer(     geom = GeomFlag, mapping = mapping,  data = data, stat = stat,      position = position, show.legend = show.legend, inherit.aes = inherit.aes,     params = list(na.rm = na.rm, ...)   ) }   set.seed(1234) d <- data.frame(x=rnorm(10), y=rnorm(10),                  country=sample(c("ar","fr"), 10, TRUE),                  stringsAsFactors = FALSE)   ggplot(d, aes(x=x, y=y, country=country, size=x)) +    geom_flag() +    scale_country() 

(output from the ggflags package)