R help - May 2009 - grid.edit() for ggplot2

Dear all,


I'm trying to access and modify grobs in a ggplot2 plot. The basic  
idea for raw Grid objects I understand from Paul Murrell's R graphics  
book, or this page of examples,

http://www.stat.auckland.ac.nz/~paul/grid/copygrob/copygrobs.R

However I can't figure out how to apply this to a ggplot (basically I  
don't know how to write a syntactically correct gPath),


p <- # minimal example
qplot(0,0)+ annotate("text",0,0,label="test")

g <- # store the plot as a grob
ggplotGrob(p)

# structure of the grob
grid.ls(g) # rather large!

# find a particular grob in the gTree
getGrob(g,"texts", grep = T)


# next step, modify, say, the colour of these grobs
grid.edit() # what do I put in here?


Thanks for any piece of advice,

baptiste

If you enter the code in this post first:
https://stat.ethz.ch/pipermail/r-help/2009-May/198791.html

then this post shows an example of how to do it with lattice:
https://stat.ethz.ch/pipermail/r-help/2009-May/199146.html

but I think there is a bug in grid since similar code does
not seem to work with your example of grid graphics
generated by ggplot2.

On Sun, May 31, 2009 at 9:01 AM, baptiste auguie <ba208 at exeter.ac.uk>
wrote:
> Dear all,
>
>
> I'm trying to access and modify grobs in a ggplot2 plot. The basic idea
for
> raw Grid objects I understand from Paul Murrell's R graphics book, or
this
> page of examples,
>
> http://www.stat.auckland.ac.nz/~paul/grid/copygrob/copygrobs.R
>
> However I can't figure out how to apply this to a ggplot (basically I
don't
> know how to write a syntactically correct gPath),
>
>
> p <- # minimal example
> qplot(0,0)+ annotate("text",0,0,label="test")
>
> g <- # store the plot as a grob
> ggplotGrob(p)
>
> # structure of the grob
> grid.ls(g) # rather large!
>
> # find a particular grob in the gTree
> getGrob(g,"texts", grep = T)
>
>
> # next step, modify, say, the colour of these grobs
> grid.edit() # what do I put in here?
>
>
> Thanks for any piece of advice,
>
> baptiste
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

Hi


baptiste auguie wrote:
> Dear all,
> 
> 
> I'm trying to access and modify grobs in a ggplot2 plot. The basic idea
> for raw Grid objects I understand from Paul Murrell's R graphics book, 
> or this page of examples,
> 
> http://www.stat.auckland.ac.nz/~paul/grid/copygrob/copygrobs.R
> 
> However I can't figure out how to apply this to a ggplot (basically I 
> don't know how to write a syntactically correct gPath),
> 
> 
> p <- # minimal example
> qplot(0,0)+ annotate("text",0,0,label="test")
> 
> g <- # store the plot as a grob
> ggplotGrob(p)
> 
> # structure of the grob
> grid.ls(g) # rather large!
> 
> # find a particular grob in the gTree
> getGrob(g,"texts", grep = T)
> 
> 
> # next step, modify, say, the colour of these grobs
> grid.edit() # what do I put in here?

(Ignoring whether this is the most ggplot-ish way to achieve the end 
result ...)

Let's take a closer look at the part of the grob (gTree) that you have 
selected ...

 > grid.ls(getGrob(g,"texts", grep = T))
texts.gTree.5
   GRID.text.3

... (the "5" and the "3" in those names are likely to be
different for
you).  This is a gTree with one child, which is a text grob.  I don't 
know much about how the "texts" gTree works, so it's not clear how
I
should modify that to influence the text grob, but I do know that I can 
modify the 'gp' component of the text grob.  For example ...

 > grid.edit("GRID.text.3", gp=gpar(col="red"))

... and if I wanted to be SURE that I was getting the text grob beneath 
that "texts" gTree, then I could use a gPath like this ...

 > grid.edit(gPath("texts.gTree.5", "GRID.text.3"),
gp=gpar(col="blue"))

... and if I wanted to use code that had a better chance of working in 
another session (when the "5" and "3" name suffixes are
likely to be
different), I could use something like ...

 > grid.edit(gPath("texts.gTree", "GRID.text"),
grep=TRUE,
             gp=gpar(col="pink"))

... does that give you what you were looking for ?

Paul

> Thanks for any piece of advice,
> 
> baptiste
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide 
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
-- 
Dr Paul Murrell
Department of Statistics
The University of Auckland
Private Bag 92019
Auckland
New Zealand
64 9 3737599 x85392
paul at stat.auckland.ac.nz
http://www.stat.auckland.ac.nz/~paul/