Вот общая идея:
# Some example data
d1 <- read.table(text = "
a b
1 2
2 8
3 4", header=T)
d2 <- read.table(text = "
a b
1 3
2 10
3 5", header=T)
# Add an identifying column to each data.frame, then 'rbind()' them together
d1 <- data.frame(host = "host1", d1)
d2 <- data.frame(host = "host2", d2)
d <- rbind(d1, d2)
# Plot the results with your graphical system of choice
library(lattice)
xyplot(b~a, group=host, data=d, type="b", auto.key=TRUE)