Question

There were example code for E on ggplot2 library:

theme_set(theme_bw())

dat = data.frame(value = rnorm(100,sd=2.5))
dat = within(dat, { 
    value_scaled = scale(value, scale = sd(value))    
obs_idx = 1:length(value)
  })

ggplot(aes(x = obs_idx, y = value_scaled), data = dat) + 
  geom_ribbon(ymin = -1, ymax = 1, alpha = 0.1) +
  geom_line() + geom_point()

There is a question: How I can make in ggplot2 my first 10 lines in red and the rest lines in blue based on example? I tried to use some kind of layer syntax is, but it doesn’t work.

Answer 1

First, add another column to your data frame dat. It has value 0 for the first 10 rows and 1 for the rest.

dat$group <- factor(rep.int(c(0, 1), c(10, nrow(dat)-10)))

Generate the plot:

library(ggplot2)

ggplot(aes(x = obs_idx, y = value_scaled), data = dat) +
geom_ribbon(ymin = -1, ymax = 1, alpha = 0.1) +
geom_line(aes(colour = group), show_guide = FALSE) +
scale_colour_manual(values = c("red", "blue")) +
geom_point()

The parameter show_guide = FALSE suppresses the legend for the red and blue lines.