[R] Converting qqplot2 qplot() to grammar?

[B. Bogart]

Hello all,

I've been using the following qplot command:

qplot(pixX,pixY, data=som, geom="tile", fill=rgb) +
scale_fill_identity() + opts(aspect.ratio = .75) + facet_grid(unitX ~ unitY)

Now I would like to convert it into the explicit ggplot grammar, so I
can remove the extras: axes, labels, background, borders, facet labels,
and extra white-space around the plot. (If anyone has suggestions on
removing these please let me know)

I've come up with the following but it is not behaving the same way as
the qplot above:

ggplot(data = somdf, mapping = aes(x = pixX, y = pixY)) +
layer(data = somdf, geom = "tile", fill=rgb) +
scale_y_continuous(name=" ",breaks=" ") +
scale_x_continuous(name=" ",breaks=" ") +
scale_fill_identity() +
coord_cartesian() +
opts(aspect.ratio = .75) +
facet_grid(unitX ~ unitY,margins=FALSE)

The result is a plot where all tiles are filled with grey50, and not the
data values. I've also tried this variation with the same results:

ggplot(data = somdf, mapping = aes(x = pixX, y = pixY)) +
geom_tile(data = somdf, fill=rgb) +
scale_y_continuous(name=" ",breaks=" ") +
scale_x_continuous(name=" ",breaks=" ") +
scale_fill_identity() +
coord_cartesian() +
opts(aspect.ratio = .75) +
facet_grid(unitX ~ unitY,margins=FALSE)

The other issue I'm having is that the above seems to create multiple
plots, another, apparently identical, plot gets drawn after I call
dev.off(). I have no idea why this would be so.

Setting name and breaks to " " seems like a hack to get rid of the axis
stuff, is there a better way?

Oh, and I can't find documentation for opts() on the ggplot2 website,
where is it available?

Thanks all, Hadley in particular,
B. Bogart