overlay two qplots (smoother and confidence intervals) in R

Question

I want to plot two sets of data and show the data, the smoother and the confidence interval for each set but both sets in one graph.

plotdata <- data.frame(x=1:10, y1=runif(10, min=0, max=10), y2=runif(10, min=10, max=20))
qplot(x, y1, data=plotdata, geom=c("point", "smooth"), method="rlm")
qplot(x, y2, data=plotdata, geom=c("point", "smooth"), method="rlm")

is there a way to combine these two qplots or to extract the qplot information and plot it with ggplot? All solutions I found so far are only for single lines, points etc but not for the confidence intervals. Thanks!

Answer 1

You can have the same plot with ggplot

E.g: the first plot:

plotdata %>% ggplot( aes(x, y1)) + geom_point() + geom_smooth(method = "rlm")

and you can play from now on with the more flexible ggplot

Answer 2

You can use gather from package tidyr to transform the data frame into the long format. This new data frame is suitable for the use with ggplot.

library(tidyr)
library(ggplot2)
library(MASS)

pd <- gather(plotdata, set, value, -x)

ggplot(pd, aes(x = x, y = value, colour = set, shape = set)) +
  geom_point() +
  geom_smooth(method = rlm)

The plot displays the data for both y1 and y2.