absoluteGrob not found (ggplot2)

Question

The function absoluteGrob {ggplot2} shows a behavior that I am not able to debug. I have ggplot2 installed and I can see the help page by ?absoluteGrob.

However, R does not find it when I try to use it:

> absoluteGrob
Error: object 'absoluteGrob' not found

More particularly, I try to execute the following code (from this answer to plot some graphs as x-labels):

library(grid)
library(ggplot2)
library(grImport)
library(igraph)


npoints <- 3

y <- rexp(npoints)
x <- seq(npoints)

pics  <- vector(mode="list", length=npoints)
for(i in 1:npoints){
  fileps <- paste0("motif",i,".ps")
  filexml <- paste0("motif",i,".xml")

  # Postscript file
  postscript(file = fileps, fonts=c("serif", "Palatino"))
  plot(graph.ring(i), vertex.label.family="serif", edge.label.family="Palatino")
  dev.off()

  # Convert to xml accessible for symbolsGrob (my_axis)
  PostScriptTrace(fileps, filexml)
  pics[i] <- readPicture(filexml)
}


my_axis <- function () {
    function(label, x = 0.5, y = 0.5, ...) {
        absoluteGrob(
           do.call("gList", mapply(symbolsGrob, pics[label], x, y, SIMPLIFY = FALSE)),
           height = unit(1.5, "cm")
      )
    }
  }

qplot(factor(c("a", "b", "c")), 1:npoints) + scale_x_discrete(labels= my_axis())

But I get the error:

Error in scale$labels(breaks) : could not find function "absoluteGrob"

Any help (or alternatives) is welcome.

ggplot2 version:

ggplot2_1.0.1

Edit

Even in the simple case...

It does not work:

library(ggplot2)
absoluteGrob

It does:

library(ggplot2)
ggplot2:::absoluteGrob

What version of `ggplot` are you using? Try updating to the newest version if you aren't on that already. — Alex A., Apr 30 '15 at 15:24
@Alex please see my edit. ggplot2:::absoluteGrob finds it. :-O — alberto, Apr 30 '15 at 15:29
Aha! Figured it out. It's in `ggplot2` but not exported. So you won't even be able to use it by `ggplot2::absoluteGrob(...)`. — Alex A., Apr 30 '15 at 15:31
mm I guess that's why if I use the ::: it raises and exception and where traceback says `stop(gettextf("'%s' is not an exported object from 'namespace:%s'", name, getNamespaceName(ns)), call. = FALSE, domain = NA)` — alberto, Apr 30 '15 at 15:45
also i am not sure the images will turn out as expected - may need a bit of manual tweaking to get the sizes reasonable: `my_g <- do.call("grobTree", Map(symbolsGrob, pics, x=c(0.2, 0.5, 0.8), y=0.5)) ; qplot(1:3, 1:3) + annotation_custom(my_g, xmin=-Inf, xmax=Inf, ymax=1.5, ymin=1 )` — user20650, Apr 30 '15 at 18:10
`annotation_custom` ! Thanks! @user20650 feel free to post this as an answer to this related question http://stackoverflow.com/questions/29939447/icons-as-x-axis-labels-in-r-ggplot2 — alberto, Apr 30 '15 at 18:16

Alex A. · Accepted Answer · 2015-04-30T17:06:48.657

The answer you linked to in your post was posted 3 years ago as of this posting, and many things in ggplot2 have changed since then. At that point, ggplot2 version 0.9.0 had not yet been released.

According to the 1.0.0 documentation for absoluteGrob, it's still experimental, which means that it was certainly experimental at the time of the linked answer. At that point it was likely exported from the ggplot2 namespace and thus available to the user. That's why the linked answer worked at the time.

However, as of version 1.0.1, it is not exported from the ggplot2 namespace. So while you're able to view the source and documentation with ggplot2:::absoluteGrob (which works for non-exported objects) and ?absoluteGrob, you will not be able to use it, even by explicitly specifying the namespace via ggplot2::absoluteGrob.

According to the source, it simply calls gTree(), which is from the grid package, with cl="absoluteGrob". You can try that in place of calling absoluteGrob() directly. For example, try the following, which will hopefully mimic the desired behavior from absoluteGrob():

grlist <- do.call("gList", mapply(symbolsGrob, pics[label], x, y, SIMPLIFY = FALSE))

gTree(children = grlist,
      cl = "absoluteGrob",
      height = unit(1.5, "cm"),
      width = NULL,
      xmin = NULL,
      ymin = NULL,
      vp = NULL)

Thanks @Alex ! And how would you call gTree? I'm trying `gTree( do.call("gList", mapply(symbolsGrob, pics[label], x, y, SIMPLIFY = FALSE)))` with no success... — alberto, Apr 30 '15 at 16:31
I'm trying hard... learning more about do.call, gList, gTree... but `unable to find an inherited method for function ‘symbolize’ for signature ‘"NULL"’` — alberto, Apr 30 '15 at 17:29
@alberto: Admittedly I don't know much about `gList` or `gTree`, but with some Googling I think it's because `gTree` isn't recognizing `"absoluteGrob"` as a class... — Alex A., Apr 30 '15 at 17:45

absoluteGrob not found (ggplot2)

1 Answers1