When creating a multiple line plot in ggplot2, how do you make one line thicker than the others?

Question

I have a simple melted data frame with 5 variables that I am plotting in a multiple line graph in ggplot2. I posted my code below and I feel the answer to this question shou

Answer 1

I've added data to make it a "reproducible example". This technique would work for the color of your lines also.

library("ggplot2")
set.seed(99)
df <- data.frame(x=c(1:5, 1:5, 1:5), y=rnorm(15, 10, 2), 
                 group=c(rep("A", 5), rep("B", 5), rep("C", 5)),
                 stringsAsFactors=FALSE)
ggplot(df, aes(x=x, y=y, group=group, colour=group)) + geom_line(size=2)

df$mysize <- rep(2, nrow(df))
df$mysize[df$group=="B"] <- 4
ggplot(df, aes(x=x, y=y, colour=group, size=mysize)) + geom_line() + 
  scale_size(range = c(2, 4), guide="none")