editGrob on a ggplotGrob returned object

[Tengfei]

Dear all,

in ggplot2 0.9.1, following code would work, but in 0.9.2, the ggplotGrob return a gtable and following code give some errors

> library(ggplot2)

> p <- qplot(wt, mpg, data = mtcars, colour = cyl, main = "title")

> g <- ggplotGrob(p)

> g <- editGrob(g, "title-2-2", gp = gpar(fontface = "italic"),

+                  grep = TRUE, global = TRUE)

Error in editGrob(g, "title-2-2", gp = gpar(fontface = "italic"), grep = TRUE,  : 

  It is only valid to edit a child of a 'gTree'

so what's the equivalent for the code above to edit a specific grob on the fly?

Thanks

Tengfei

[Winston Chang]

g is a gtable object. You can inspect it with the following:

# Show the structure of the gtable object, but don't recurse into sub-components
str(g, max.level=1)

# Print the data frame recording layout
g$layout

# Get the list of grobs in the gtable
g$grobs

# Get a 1x1 gtable that contains just the title
g[2,4]



This code will have the effect you're looking for. It might be worth
thinking about how to modify the gtable API to make this sort of
access easier.

library(ggplot2)
library(grid)
library(gtable)
p <- qplot(wt, mpg, data = mtcars, colour = cyl, main = "Title text")
g <- ggplotGrob(p)

# Get index of the title grob
idx <- which(g$layout$name == "title")

# Modify the title grob and save it back
g$grobs[[idx]] <- editGrob(g$grobs[[idx]], gp = gpar(fontface =
"italic", col="red"))

grid.draw(g)



It would also be nice to be able to do something like grid.ls() on a
gtable and get back a useful result.

-Winston

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[Tengfei Yin]

On Tue, Sep 4, 2012 at 11:29 PM, Winston Chang <winsto...@gmail.com> wrote:

g is a gtable object. You can inspect it with the following:

# Show the structure of the gtable object, but don't recurse into sub-components
str(g, max.level=1)

# Print the data frame recording layout
g$layout

# Get the list of grobs in the gtable
g$grobs

# Get a 1x1 gtable that contains just the title
g[2,4]



This code will have the effect you're looking for. It might be worth
thinking about how to modify the gtable API to make this sort of
access easier.

Yes, a more easier API would be nice. 

library(ggplot2)
library(grid)
library(gtable)
p <- qplot(wt, mpg, data = mtcars, colour = cyl, main = "Title text")
g <- ggplotGrob(p)

# Get index of the title grob
idx <- which(g$layout$name == "title")

# Modify the title grob and save it back
g$grobs[[idx]] <- editGrob(g$grobs[[idx]], gp = gpar(fontface =
"italic", col="red"))

grid.draw(g)

 

Thanks a lot for this clear elucidation and the examples!

Tengfei  

--
Tengfei Yin
MCDB PhD student
1620 Howe Hall, 2274,
Iowa State University
Ames, IA,50011-2274