在ggplot图例中隐藏未使用的级别

install.packages("ggplot2")

library(ggplot2)

data <- data.frame(
  x = c("A", "B", "C", "D"),
  y = c(1, 2, 3, 4),
  group = c("Group 1", "Group 2", "Group 1", "Group 2")
)

p <- ggplot(data, aes(x = x, y = y, fill = group)) +
  geom_bar(stat = "identity")

p + guides(fill = guide_legend(override.aes = list(fill = "transparent")))