plotting multiple plots in ggplot2 on same graph that are unrelated

Question

How would one use the smooth.spline() method in a ggplot2 scatterplot?

If my data is in the data frame called data, with two columns, x and y.

The smooth.spline would be sm <- smooth.spline(data$x, data$y). I believe I should use geom_line(), with sm$x and sm$y as the xy coordinates. However, how would one plot a scatterplot and a lineplot on the same graph that are completely unrelated? I suspect it has something to do with the aes() but I am getting a little confused.

Answer 1

You can use different data(frames) in different geoms and call the relevant variables using aes or you could combine the relevant variables from the output of smooth.spline

# example data
set.seed(1)
dat <- data.frame(x = rnorm(20, 10,2))
dat$y <- dat$x^2 - 20*dat$x + rnorm(20,10,2)

# spline
s <- smooth.spline(dat)

# plot - combine the original x & y and the fitted values returned by 
# smooth.spline into a data.frame

library(ggplot2)

ggplot(data.frame(x=s$data$x, y=s$data$y, xfit=s$x, yfit=s$y)) +
                      geom_point(aes(x,y)) + geom_line(aes(xfit, yfit))

# or you could use geom_smooth    
ggplot(dat, aes(x , y)) + geom_point() + geom_smooth()