How to add a label with directlabels when using multiple geoms?

I'm struggling to create labels at the right end of a line plot with directlabels when I'm using more than one geom. Here is an example:

#load packages
library(dplyr)
library(ggplot2)
library(tidyr)
library(directlabels)

#create data
set.seed(1)
test <- tibble(year = as.factor(rep(1990:2000, 4)), 
     label = rep(replicate(4, paste0(sample(letters, 20), collapse = "")), each =11), #create long random labels
     value = rnorm(44))
test[which(test$year==2000),]$value <- seq(0,0.1, length.out = 4) # make final values very similar

average <- test %>% 
     group_by(year) %>% 
     summarize(value = mean(value)) %>% 
     bind_cols(label = "average")

#draw plot
ggplot(test, aes(x = year, y = value, group = label, color = label)) +
  geom_line() +
  geom_smooth(data = average,
              mapping = aes(x = year, y = value, group = label, color = label),
              inherit.aes = F, col = "black") +
  geom_dl(aes(label = label,
              color = label), 
          method = list(dl.combine("last.bumpup"))) +
  theme(legend.position = "none")

This gives this plot:

Now I'm looking to add a black-colored label at the right of the geom_smooth line that says "average". One of the problems I found with some of the methods I've tried is that it overlaps with the other labels when I create it separately and that it does not show up in black.

For example:

ggplot(test, aes(x = year, y = value, group = label, color = label)) +
  geom_line() +
  geom_smooth(data = average,
              mapping = aes(x = year, y = value, group = label, color = label),
              inherit.aes = F, col = "black") +
  geom_dl(aes(label = label,
              color = label), 
          method = list(dl.combine("last.bumpup"))) +
  geom_dl(data = average,
          mapping = aes(label = label,
              color = label), 
          method = list(dl.combine("last.bumpup"))) +
  theme(legend.position = "none")

gives this plot:

To summarize, I'm looking to create a label for geom_smooth that has the same color as the geom_smooth line and does not collide with the other labels.

One caveat: I can't use the stat_summary (as proposed elsewhere) because in my actual data, the average is weighted and since I don't know the weights, I can't go from individual data points to the average. So I need to take the averages provided in the dataframe.

Update

In my actual data, the labels are much longer (10-30 characters) and some of them have very similar y-values at the highest year. This is why I used directlabels with the bumpup argument. There will likely be overlap if the labels don't repel each other.

Solution

Try using ggrepel as an alternative to directlabels.

(Updated approach following revised question)

Note it might be more elegant to include the average data line and label in the test data adapted for labelling. This approach requires some manual tweaking for the "Average" label. There are other geom_text_repel() arguments not used which might allow improvement of positioning.

library(dplyr)
library(ggplot2)
library(tidyr)
library(ggrepel)

set.seed(1)
test <- tibble(year = as.factor(rep(1990:2000, 4)), 
               label = rep(replicate(4, paste0(sample(letters, 20), collapse = "")), each =11), #create long random labels
               value = rnorm(44))
test[which(test$year==2000),]$value <- seq(0,0.1, length.out = 4) # make final values very similar

average <- test %>% 
  group_by(year) %>% 
  summarize(value = mean(value)) %>% 
  bind_cols(label = "average")


# initial plot with labels for lines
# For fuller description of possible arguments to repel function, see:
# https://ggrepel.slowkow.com/articles/examples.html
p <- 
  ggplot(test, aes(x = year, y = value, group = label, color = label)) +
  geom_line() +
  geom_smooth(data = average,
              mapping = aes(x = year, y = value, group = label, color = label),
              inherit.aes = F, col = "black") +
  geom_text_repel(data = filter(test, year == 2000), 
                  aes(label = label,
                      color = label),
                  direction = "y",
                  vjust = 1.6,
                  hjust = 0.5,
                  segment.size = 0.5,
                  segment.linetype = "solid",
                  box.padding = 0.4,
                  seed = 123) +
  coord_cartesian(clip = 'off')+
  scale_x_discrete(expand = expansion(mult = c(0.06, 0.0)))+
  theme(legend.position = "none",
        plot.margin = unit(c(5, 50, 5, 5), "mm"))
  
# find coordinates for last point of geom_smooth line, by inspection of ggplot_buildt

lab_avg <- 
  slice_tail(ggplot_build(p)$data[[2]], n = 1) %>% 
  mutate(label = "Average")

# plot with label for geom_smooth line
# positioning of the Average label achieved manually varying vjust and hjust,
# there is probably a better way of doing this

p1 <- 
  p + 
  geom_text_repel(data = lab_avg,
          aes(x = x, y = y, label = label),
          colour = "black",
          direction = "y",
          vjust = 3.5,
          hjust = -7,
          segment.size = 0.5,
          segment.linetype = "solid",
          segment.angle = 10,
          box.padding = 0.4,
          seed = 123)
p1

^{Created on 2021-08-22 by the reprex package (v2.0.0)}

Initial answer to original question.

You could try with geom_text() using data from the average dataset and adjusting the location of "Average" using hjust and vjust.

Use scale_x_discrete(expand...) to create a bit of extra space for the text label.


ggplot(test, aes(x = year, y = value, group = label, color = label)) +
  geom_line() +
  geom_smooth(data = average,
              mapping = aes(x = year, y = value, group = label, color = label),
              inherit.aes = F, col = "black") +
  geom_dl(aes(label = label,
              color = label), 
          method = list(dl.combine("last.bumpup"))) +
  scale_x_discrete(expand = expansion(mult = c(0.06, 0.2)))+
  geom_text(data = slice_tail(average, n = 1),
            aes(x = year, y = value, label = "Average"),
            colour = "black",
            hjust = -0.2,
            vjust = 1.5)+
  theme(legend.position = "none")

^{Created on 2021-08-21 by the reprex package (v2.0.0)}