How to plot geom_point alone plus geom_point with position_dodge - r

Question

I struggling on how I can plot my real values, present in the real_values vector, next to the estimates values. My problem here is that the estimates values have a range (via the geom_errorbar), and for the real values I would like to plot just the point, in black, on the left side of each of the 10 estimates.
Here's an example of what I tried:
est_values = rnorm(20)
real_values = rnorm(10)
dat_ex = data.frame(
xvalues = 1:10,
values = est_values,
method = c(rep("A",10),rep("B",10)),
ic_0.025 = c(est_values - rnorm(20,1,0.1)),
ic_0.975 = c(est_values + rnorm(20,1,0.1)))
ggplot(dat_ex) +
#geom_point(aes(x = 1:10, y= real_values), size = 2) +
geom_point(aes(x = xvalues, y= values, group = method, colour = method), position=position_dodge(.9), size = 3) +
geom_errorbar(aes(x = xvalues, y= values, group = method, colour = method,ymin = ic_0.025, ymax = ic_0.975), size = 1.3,position=position_dodge(.9), width = .2)

Answer 1

ggplot generally works best with data in data frames. So we put your real_values in a data frame and plot them in a separate layer, and "nudge" them to the left, as requested:
ggplot(dat_ex) +
geom_point(aes(x = xvalues, y= values, group = method, colour = method), position=position_dodge(.9), size = 3) +
geom_errorbar(aes(x = xvalues, y= values, group = method, colour = method,ymin = ic_0.025, ymax = ic_0.975), size = 1.3,position=position_dodge(.9), width = .2) +
geom_point(
data = data.frame(values = real_values, xvalues = dat_ex$xvalues),
aes(x = xvalues, y = values),
position = position_nudge(x = -.4),
color = "black")
A nicer method might be to put them all in the same data frame. This can simplify the code and will automatically put them in the legend.
library(dplyr)
dat_ex = data.frame(
xvalues = 1:10,
values = real_values,
method = "real"
) %>%
bind_rows(dat_ex) %>%
mutate(method = factor(method, levels = c("real", "A", "B")))
ggplot(dat_ex, aes(x = xvalues, y = values, color = method)) +
geom_point(position=position_dodge(.9), size = 3) +
geom_errorbar(aes(ymin = ic_0.025, ymax = ic_0.975, group = method),
size = 1.3, position=position_dodge(.9), width = .2) +
scale_color_manual(values = c("real" = "black", "A" = "orange", "B" = "blue"))

Answer 2

I would add real_values to your data as another level of method, so they will be dodged along with "A" and "B" (and included in the legend):
library(ggplot2)
dat_ex <- rbind(
dat_ex,
data.frame(
xvalues = 1:10,
values = real_values,
method = "Real",
ic_0.025 = NA_real_,
ic_0.975 = NA_real_
)
)
# arrange so "Real" is on the left
dat_ex$method <- factor(dat_ex$method, levels = c("Real", "A", "B"))
ggplot(dat_ex) +
geom_point(aes(x = xvalues, y= values, group = method, colour = method), position=position_dodge(.9), size = 3) +
geom_errorbar(aes(x = xvalues, y= values, group = method, colour = method,ymin = ic_0.025, ymax = ic_0.975), size = 1.3,position=position_dodge(.9), width = .2) +
scale_colour_manual(values = c("black", "forestgreen", "royalblue"))