[R] loess lines in xyplot with two or more variables on the left side of a formula

[Chuck Cleland]

Hello:
  I recall something like this being discuss recently, but I can't seem
to locate an example in the archives.  I have data like the following:

df <- expand.grid(1:4, 1992:2002)
names(df) <- c("MSA", "YEAR")
df$IDUPREV <- runif(44)
df$VALIDAT <- rnorm(44)

  I want to create an xyplot() with separate loess lines for each series
(IDUPREV and VALIDAT) in the same panel.  I'm able to plot each series
in the same panel like this:

library(lattice)

xyplot(IDUPREV + VALIDAT ~ YEAR | MSA, data = df,
       panel = panel.superpose, type="l")

  How could I change that so that panel.loess() is applied separately to
each series?

thanks,

Chuck Cleland

-- 
Chuck Cleland, Ph.D.
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