Lattice: Plotting two lines with different scale and axes in the same panel

Question

I have something like this:

a <- c(1,4,2,8)
b <- c(100,80,40, 0)
c <- 1:4
x <- rep("foo",4)
y <- rep("bar",4)

df1 <- data.frame(c, y = a, gr = x)
df2 <- data.frame(c, y = b, gr = y)
df <- rbind(df1,df2)

xyplot(y ~ c, data = df, type = "l", group = df$gr)

Results in this:

I am looking for a way that would allow me to change the scale so that the blue line fills the entire panel area, and add a corresponding axis to the right side of the plot.

If adding the axis is too hard, then it is not a requirement. The units on the y axis are arbitrary anyway (in my own data). Maybe a way to normalize the data would work?

There are several answers on this site, but they all work on the basic graphics of R, and none using lattice.

Answer 1

Is it what you want?

library(latticeExtra)
library(dplyr)
dfgr <-df %>% filter(gr == "foo")
dfbar <-df %>% filter(gr == "bar")
obj1 <- xyplot(y ~ c, dfgr, type = "l")
obj2 <- xyplot(y ~ c, dfbar, type = "l")
doubleYScale(obj1, obj2, add.ylab2 = TRUE)