Merging or overlaying xyplots in a lattice panel

Question

Trying to figure out how to add points or a data series to an existing lattice panel once it's been created. Does this have something to do with plot.points and/or the update function?

# Initialize first plot
library(lattice)
a <- xyplot(Sepal.Length~Sepal.Width, groups=Species, data=iris
            , subset=Species %in% levels(Species)[1:2])
print(a) 

# Create second plot to overlay or merge with the first plot
b <- xyplot(Sepal.Length~Sepal.Width, groups=Species, data=iris
            , subset=Species %in% levels(Species)[3])

# Initial attempt at merging plots:
library(latticeExtra)
print(c(a,b)) # this displays the data in an adjacent second panel
print(c(a,b,layout=c(1,1))) # and this only shows series "b"

Note: in this example, both plots "a" and "b" come from the original iris dataframe, but ideally, the solution would work with distinct dataframes.

Any ideas? Thanks!
Bryan

Answer 1

You're looking for as.layer, I think; try this. It's in the latticeExtra library as well.

library(latticeExtra)
a + as.layer(b)

See documentation here: http://latticeextra.r-forge.r-project.org/#as.layer