QQ plot: More than two data

Question

I wanted to graph a QQ plot similar to this picture:

I managed to get a QQ plot using two samples, but I do not know how to add a third one to the plot. Here is my result:

Here is the code I used:

qqplot(table$Bedouin, table$Tunisia, xlim = c(-0.25,0.25), ylim = c(-025,0.25))

In my table data frame I have other populations I would like to add. But I can't.

Thank you in advance.

Answer 1

I suppose you're looking for a scatterplot of sorted values since all variables are stored in the same data frame.

An example dataset:

set.seed(10)
dat <- data.frame(A = rnorm(20), B = rnorm(20), C = rnorm(20))

This is a way to create the plot with basic R functions:

# create a QQ-plot of B as a function of A
qqplot(dat$A, dat$B, xlim = range(dat), ylim = range(dat), 
       xlab = "A", ylab = "B/C")
# create a diagonal line
abline(a = 0, b = 1)
# add the points of C
points(sort(dat$A), sort(dat$C), col = "red")
# create a legend
legend("bottomright", legend = c("B", "C"), pch = 1, col = c("black", "red"))