How to make dodge in geom_bar agree with dodge in geom_errorbar, geom_point

Question

I have a dataset where measurements are made for different groups at different days.

I want to have side by side bars representing the measurements at the different

Answer 1

The first change I reformatted the code according to the advanced R style guide.

days <- data.frame(day=c(0,1,8,15))

groups <- data.frame(
    group=c("A","B","C","D", "E"), 
    means=seq(0,1,length=5)
    )

my_data <- merge(days, groups)

my_data$mid <- exp(my_data$means+rnorm(nrow(my_data), sd=0.25))
my_data$sigma <- 0.1

Now when we look at the data we see that day is a factor and everything else is the same.

str(my_data)

To remove blank space from the plot I converted the day column to factors. CHECK that the levels are in the proper order before proceeding.

my_data$day <- as.factor(my_data$day) 
levels(my_data$day)

The next change I made was defining y in your aes arguments. As I'm sure you are aware, this lets ggplot know where to look for y values. Then I changed the position argument to "dodge" and added the stat="identity" argument. The "identity" argument tells ggplot to plot y at x. geom_errorbar inherits the dodge position from geom_bar so you can leave it unspecified, but geom_point does not so you must specify that value. The default dodge is position_dodge(.9).

ggplot(data = my_data, 
 aes(x=day,
     y= mid, 
     ymin=mid-sigma, 
     ymax=mid+sigma,       
     fill=group)) +
   geom_bar(position="dodge", stat = "identity") + 
   geom_errorbar( position = position_dodge(), colour="black") +
   geom_point(position=position_dodge(.9), aes(y=mid, colour=group))