two scatter plots in one

# first create a data.frame in the long format containing the two  
data sets
x1 <- seq(-10, 10)
x2 <- seq(-8, 12)
y1 <- sin(x1/3)
y2 <- cos(x2/2)

d1 <- data.frame(x=x1, y=y1, var="1")
d2 <- data.frame(x=x2, y=y2, var="2")

library(reshape)
d <- melt(merge(d1, d2, all=T), id=c("x", "var"))

 # here goes the plotting in a high-level perspective

library(ggplot2)

qplot(x, value, data=d, geom=c("line","point"), colour=var)

or,

library(lattice)

xyplot(value ~ x, data=d, type="b", groups = var)

liujb wrote:

Dear R users,

I need to compare two scatter plots,
plot(x1, y1)
plot(x2, y2)

and would like to plot them in the same figure. How do I do it?

Hi liujb,
How about this:

plot(x1,y1,xlim=range(c(x1,x2)),ylim=range(c(y1,y2)),col="red")
points(x2,y2,col="blue")


Jim