relative placement of annotations

[gdkrmr]

Feature request:
It would be really useful if annotations could be placed like legends indicating their relative position (legend.placement = c(1,0)) in the plot area.

Coordinate limits can be extracted after building the plot:
https://gist.github.com/tomhopper/9076152

Being able to do this before building the plot would be a really neat feature, e.g. for placing regression formulae nicely in a corner.
Something like:

g + annotate("text", x = get_xlim()[2], y = get_ylim()[2], label = "y = 3 + 4x")

[hadley]

You can already do it :) (for that special case)

library(ggplot2)
ggplot(mpg, aes(displ, hwy)) + 
  geom_point() + 
  annotate("text", -Inf, Inf, label = "Top-left", hjust = 0, vjust = 1)

[gdkrmr]

Thanks, I wasn't aware of that!

[gdkrmr]

@hadley btw. this feature is missing in the documentation

[hadley]

It's in the book ;)

[baptiste]

the trick also applies to annotation_custom; while answering it the thought occurred to me that one could define complex positions, such as x = 1 - 2i, which would mean "2 data units to the left of the right edge". (actually, I was thinking of absolute vs relative grid units, but it's a similar idea). Claudia B. inspired this with her hyperSpec package, where complex numbers are used to encode similarly dual information.

Just throwing the idea out there, just in case :)

[kendonB]

Making this explicit and separated by axis would be a welcome addition. For example, I'd like to be able to choose the x-value of an annotation explicitly and have the y-value 50% up the plot.

[baptiste]

@kendonB qplot(1:10,1:10, geom="blank") + annotation_custom(textGrob("y centered"),xmin=3,xmax=3)

[kendonB]

Thanks so much @baptiste. Is there any way to also have hjust/vjust in this?

[colinbrislawn]

It would be really useful if annotations could be placed like legends indicating their relative position (legend.placement = c(1,0)) in the plot area.

I agree!

annotate("text", -Inf, Inf, ...

That solution will place a annotation into every facet, where legend.placement places a single annotation based on the relative position in the graph, regardless of the other geoms or facets being used.

I would like to see something like annotate_relative or annotate_global to provide this functionality.

[baptiste]

annotation_custom provides a way by wrapping an arbitrary grob in a gTree that spans the full panel. The syntax is not super convenient, especially since one has to load grid to use unit and gTree, but there could be a convenience function around this.

library(ggplot2)
library(grid)

g <- grobTree(textGrob('here', x=unit(0.8, "npc"), y=unit(0.5,"npc")))
qplot(0:10,0:10) +
  annotate("point",x=8,y=5,col="red") +
  annotation_custom(g)

To specify specific facets, one would need a geom_custom, which exists as proof-of-principle in egg, but not on CRAN because ggplot2 internal changes in layout.

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