# [R] Drawing rectangles in multiple panels

Stephen Tucker brown_emu at yahoo.com
Thu Jul 12 03:53:28 CEST 2007

```Not that Trellis/lattice was entirely easy to learn at first. :)

I've been playing around with ggplot2 and there is a plot()-like wrapper for
building a quick plot [incidentally, called qplot()], but otherwise it's my
understanding that you superpose elements (incrementally) to build up to the
graph you want. Here is the same plot in ggplot2:

rectInfo <-
list(matrix(runif(4), 2, 2),
matrix(runif(4), 2, 2),
matrix(runif(4), 2, 2))

library(ggplot2)
ggopt(grid.fill = "white") # just my preference
## original plot of points
p <-
qplot(x,y,data=data.frame(x=runif(30),y=runif(30),f=gl(3,30)),facets=f~.)
# print(p)

## external data (rectangles) -> in coordinates for geom_polygon
x <- do.call(rbind,
mapply(function(.r,.f)
data.frame(x=.r[c(1,1,2,2),1],y=.r[c(1,2,2,1),2],f=.f),
.r=rectInfo,.f=seq(along=rectInfo),SIMPLIFY=FALSE))
## add rectangle to original plot of points
p+layer(geom="polygon",data=x,mapping=aes(x=x,y=y),facets=f~.)
# will print the graphics on my windows() device

Though lattice does seem to emphasize the 'chart type' approach to graphing,
in a way I see that it provides a similar flexibility - just that the
specifications for each element are contained in functions and objects that
are ultimately invoked by a high-level/higher-order function, instead of
being combined in the linear fashion of ggplot2.

ST

--- Deepayan Sarkar <deepayan.sarkar at gmail.com> wrote:

> On 7/11/07, hadley wickham <h.wickham at gmail.com> wrote:
> > > A question/comment: I have usually found that the subscripts argument
> is
> > > what I need when passing *external* information into the panel
> function, for
> > > example, when I wish to add results from a fit done external to the
> trellis
> > > call. Fits[subscripts] gives me the fits (or whatever) I want to plot
> for
> > > each panel. It is not clear to me how the panel layout information from
> > > panel.number(), etc. would be helpful here instead. Am I correct? -- or
> is
> > > there a smarter way to do this that I've missed?
> >
> > This is one of things that I think ggplot does better - it's much
> > easier to plot multiple data sources.  I don't have many examples of
> > this yet, but the final example on
> > http://had.co.nz/ggplot2/geom_abline.html illustrates the basic idea.
>
> That's probably true. The Trellis approach is to define a plot by
> "data source" + "type of plot", whereas the ggplot approach (if I
> understand correctly) is to create a specification for the display
> (incrementally?) and then render it. Since the specification can be
> very general, the approach is very flexible. The downside is that you
> need to learn the language.
>
> On a philosophical note, I think the apparent limitations of Trellis
> in some (not all) cases is just due to the artificial importance given
> to data frames as the one true container for data. Now that we have
> proper multiple dispatch in S4, we can write methods that behave like
> traditional Trellis calls but work with more complex data structures.
> We have tried this in one bioconductor package (flowViz) with
> encouraging results.
>
> -Deepayan
>
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