Adding trend lines/boxplots (by group) in ggplot2
- by Tal Galili
Hi all,
I have 40 subjects, of two groups, over 15 weeks, with some measured variable (Y).
I wish to have a plot where: x = time, y = T, lines are by subjects and colours by groups.
I found it can be done like this:
TIME <- paste("week",5:20)
ID <- 1:40
GROUP <- sample(c("a","b"),length(ID), replace = T)
group.id <- data.frame(GROUP, ID)
a <- expand.grid(TIME, ID)
colnames(a) <-c("TIME", "ID")
group.id.time <- merge(a, group.id)
Y <- rnorm(dim(group.id.time)[1], mean = ifelse(group.id.time$GROUP =="a",1,3) )
DATA <- cbind(group.id.time, Y)
qplot(data = DATA,
x=TIME, y=Y,
group=ID,
geom = c("line"),colour = GROUP)
But now I wish to add to the plot something to show the difference between the two groups (for example, a trend line for each group, with some CI shadelines) - how can it be done?
I remember once seeing the ggplot2 can (easily) do this with geom_smooth, but I am missing something about how to make it work.
Also, I wondered at maybe having the lines be like a boxplot for each group (with a line for the different quantiles and fences and so on). But I imagine answering the first question would help me resolve the second.
Thanks.
