Limiting vertical line length in R ggplot2

Question

I am trying to draw a forest plot with different groups. The code I'm using looks like the following:

d = data.frame(Estimate = c(1.8,1.9,2.1,2.4,2.7,2.5), 
               Group = rep(c('Group A', 'Group B'), each = 3),
               Method = rep(c('Method 1', 'Method 2', 'Method 3'), 2))
d$Lower = d$Estimate - 0.3
d$Upper = d$Estimate + 0.3
ggplot(data = d, aes(y = Group, x = Estimate, xmin = Lower, xmax = Upper, color = Method)) + 
  geom_point(size = 2, position=position_dodge(width = 0.5)) + 
  geom_linerange(position=position_dodge(width = 0.5)) + 
  geom_vline(xintercept = c(2, 2.5), linetype = "dashed")

And the resulting plot:

The vertical lines (2, 2.5) are the true group means. I want to limit these vertical lines to be within each group (i.e., the first one from bottom to the middle, the second one middle to top). Anyone know how to do this?

I've tried geom_segment() function but I think it requires a numerical y input, while it's a factor here.

Answer 1

Factors plotted on an axis are "really" numeric, but with labels added, so you can go ahead and add numeric segments:

ggplot(data = d, aes(y = Group, x = Estimate, xmin = Lower, xmax = Upper, 
                     color = Method)) + 
  geom_point(size = 2, position=position_dodge(width = 0.5)) + 
  geom_linerange(position=position_dodge(width = 0.5)) + 
  geom_segment(data = data.frame(y = c(0.67, 1.67), x = c(2, 2.5), 
                                 xend = c(2, 2.5),  yend = c(1.33, 2.33)), 
               aes(x, y, xend = xend, yend = yend),
               inherit.aes = FALSE, linetype = 2) 

Or, with a few tweaks:

ggplot(data = d, aes(y = Group, x = Estimate, xmin = Lower, xmax = Upper, 
                     color = Method)) + 
  geom_linerange(position=position_dodge(width = 0.5), size = 1) + 
  geom_point(size = 3, position=position_dodge(width = 0.5), shape = 21,
             fill = "white") + 
  geom_segment(data = data.frame(y = c(0.67, 1.67), x = c(2, 2.5), 
                                 xend = c(2, 2.5),  yend = c(1.33, 2.33)), 
               aes(x, y, xend = xend, yend = yend),
               inherit.aes = FALSE, linetype = 2) +
  annotate("text", c(2, 2.5), c(1.5, 2.5), size = 6,
           label = c("Group mean = 2", "Group mean = 2.5")) +
  theme_minimal(base_size = 20) +
  scale_color_brewer(palette = "Set1")