这里有一个方法来实现你想要的。然而，正如@AllanCameron在评论中提到的，这种方法的适当性 * 严重 * 依赖于数据。我已经包括了额外的例子来说明潜在的问题。
该方法包括计算每个组的平均xy，然后再创建两个三角形：一个用于线（df 1），一个用于标签（df 2）：

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

# Your example data (Example1): IMPORTANT: note modified x and y column names,
# you will first need to change your x and y columns to x_1 and y_1
df <- data.frame(
  group = c("A", "A", "B", "B"),
  x_1 = c(1, 2, 3, 4),
  y_1 = c(2, 3, 4, 5)
)

# Create df for plotting lines from original points to group's mean point
df1 <- df %>%
  group_by(group) %>%
  mutate(x_2 = mean(x_1),
         y_2 = mean(y_1)) %>%
  pivot_longer(-group,
               names_to = c(".value", "var"),
               names_sep = "_")

# Create df for single group label
df2 <- df %>%
  group_by(group) %>%
  mutate(x_2 = mean(x_1),
         y_2 = mean(y_1)) %>%
  select(-ends_with("1")) %>%
  distinct()

# Plot
ggplot() +
  geom_path(data = df1,
            aes(x, y, group = group),
            colour = "grey") +
  geom_point(data = df,
             aes(x_1, y_1),
             size = 2) +
  geom_text(data = df2,
            aes(x_2, y_2, label = group),
            size = 5)

字符串
现在考虑这两个其他的示例框架：

# Example2
df <- data.frame(
  group = rep(c("A", "B"), each = 3),
  x_1 = c(1, 1.5, 2, 3, 3.5, 4),
  y_1 = c(2, 4, 3, 4, 2.5, 5)
)

# Example3
set.seed(1)
df <- data.frame(group = rep(c("A", "B", "C"), each = 10),
                 x_1 = runif(n = 30, min = 1, max = 4),
                 y_1 = runif(n = 30, min = 2, max = 5))

型
x1c 0d1x的数据
Example 1和Example 2看起来不错，但您提出的方法不能很好地扩展像Example 3这样的数据。每个组的线交叉，这使得解释变得困难。如果您的完整数据更复杂，并且包含很多像Example 3这样的点，使用颜色（或形状）在传达数据中发生的事情方面要有效得多：

ggplot() +
  geom_point(data = df,
             aes(x_1, y_1, colour = group),
             size = 2) +
  labs(x = "x", y = "y")

型

的