Create dynamic labels for geom_smooth lines - r

Question

I have a changing df and I am grouping different values c.
With ggplot2 I plot them with the following code to get a scatterplott with multiple linear regression lines (geom_smooth)
ggplot(aes(x = a, y = b, group = c)) +
geom_point(shape = 1, aes(color = c), alpha = alpha) +
geom_smooth(method = "lm", aes(group = c, color = c), se = F)
Now I want to display on each geom_smooth line in the plot a label with the value of the group c.
This has to be dynamic, because I can not write new code when my df changes.
Example: my df looks like this
a b c
----------------
1.6 24 100
-1.4 43 50
1 28 100
4.3 11 50
-3.45 5.2 50
So in this case I would get 3 geom_smooth lines in the plot with different colors.
Now I simply want to add a text label to the plot with "100" next to the geom_smooth with the group c = 100 and a text label with "50"to the line for the group c = 50, and so on... as new groups get introduced in the df, new geom_smooth lines are plotted and need to be labeled.
the whole code for the plot:
ggplot(aes(x = a, y = b, group = c), data = df, na.rm = TRUE) +
geom_point(aes(color = GG, size = factor(c)), alpha=0.3) +
scale_x_continuous(limits = c(-200,2300))+
scale_y_continuous(limits = c(-1.8,1.5))+
geom_hline(yintercept=0, size=0.4, color="black") +
scale_color_distiller(palette="YlGnBu", na.value="white") +
geom_smooth(method = "lm", aes(group = factor(GG), color = GG), se = F) +
geom_label_repel(data = labelInfo, aes(x= max, y = predAtMax, label = label, color = label))

Answer 1

You can probably do it if you pick the location you want the lines labelled. Below, I set them to label at the far right end of each line, and used ggrepel to avoid overlapping labels:
library(ggplot2)
library(ggrepel)
library(dplyr)
set.seed(12345)
df <-
data.frame(
a = rnorm(100,2,0.5)
, b = rnorm(100, 20, 5)
, c = factor(sample(c(50,100,150), 100, TRUE))
)
labelInfo <-
split(df, df$c) %>%
lapply(function(x){
data.frame(
predAtMax = lm(b~a, data=x) %>%
predict(newdata = data.frame(a = max(x$a)))
, max = max(x$a)
)}) %>%
bind_rows
labelInfo$label = levels(df$c)
ggplot(
df
, aes(x = a, y = b, color = c)
) +
geom_point(shape = 1) +
geom_smooth(method = "lm", se = F) +
geom_label_repel(data = labelInfo
, aes(x= max
, y = predAtMax
, label = label
, color = label))

Answer 2

This method might work for you. It uses ggplot_build to access the rightmost point in the actual geom_smooth lines to add a label by it. Below is an adaptation that uses Mark Peterson's example.
library(ggplot2)
library(ggrepel)
library(dplyr)
set.seed(12345)
df <-
data.frame(
a = rnorm(100,2,0.5)
, b = rnorm(100, 20, 5)
, c = factor(sample(c(50,100,150), 100, TRUE))
)
p <-
ggplot(df, aes(x = a, y = b, color = c)) +
geom_point(shape = 1) +
geom_smooth(method = "lm", se = F)
p.smoothedmaxes <-
ggplot_build(p)$data[[2]] %>%
group_by( group) %>%
filter( x == max(x))
p +
geom_text_repel( data = p.smoothedmaxes,
mapping = aes(x = x, y = y, label = round(y,2)),
col = p.smoothedmaxes$colour,
inherit.aes = FALSE)

Answer 3

This came up for me today and I landed on this solution with data = ~fn()
library(tidyverse)
library(broom)
mpg |>
ggplot(aes(x = displ, y = hwy, colour = class, label = class)) +
geom_count(alpha = 0.1) +
stat_smooth(alpha = 0.6, method = lm, geom = "line", se = FALSE) +
geom_text(
aes(y = .fitted), size = 3, hjust = 0, nudge_x = 0.1,
data = ~{
nest_by(.x, class) |>
summarize(broom::augment(lm(hwy ~ displ, data = data))) |>
slice_max(order_by = displ, n = 1)
}
) +
scale_x_continuous(expand = expansion(add = c(0, 1))) +
theme_minimal()
Or do it with a function
#' #examples
#' last_lm_points(df = mpg, formula = hwy~displ, group = class)
last_lm_points <- function(df, formula, group) {
# df <- mpg; formula <- as.formula(hwy~displ); group <- sym("class");
x_arg <- formula[[3]]
df |>
nest_by({{group}}) |>
summarize(broom::augment(lm(formula, data = data))) |>
slice_max(order_by = get(x_arg), n = 1)
}
mpg |>
ggplot(aes(displ, hwy, colour = class, label = class)) +
geom_count(alpha = 0.1) +
stat_smooth(alpha = 0.6, method = lm, geom = "line", se = FALSE) +
geom_text(
aes(y = .fitted), size = 3, hjust = 0, nudge_x = 0.1,
data = ~last_lm_points(.x, hwy~displ, class)
) +
scale_x_continuous(expand = expansion(add = c(0, 1))) +
theme_minimal()