add the same density curve to a plot in R

Question

I was wondering how I could add the same density curve to an xyplot() from lattice package in R ( see reproducible code below )?

library(lattice)

xyplot((1:32*.01)~wt|gear , data = mtcars)

lines(density(rnorm(1e3, 3.5))) # add this to all plot panes in `xyplot` above

Answer 1

We could use layer

library(lattice)
library(latticeExtra)
foo <- xyplot((1:32*.01)~wt|gear , data = mtcars)
foo + 
      layer(panel.densityplot(rnorm(1e3, 3.5), plot.points = FALSE))