如何通过ggplot2添加数据中不存在的图例类别

library(ggplot2)

df <- data.frame(
  x = c(1, 2, 3, 4, 5),
  y = c(2, 4, 6, 8, 10),
  category = c("A", "B", "C", "D", "E")
)

p <- ggplot(df, aes(x = x, y = y, color = category)) +
  geom_point()

p <- p + scale_color_manual(values = c("A" = "red", "B" = "blue", "C" = "green", "D" = "purple", "E" = "orange"))

p <- p + labs(color = "Category")

library(ggplot2)

df <- data.frame(
  x = c(1, 2, 3, 4, 5),
  y = c(2, 4, 6, 8, 10),
  category = c("A", "B", "C", "D", "E")
)

p <- ggplot(df, aes(x = x, y = y, color = category)) +
  geom_point() +
  scale_color_manual(values = c("A" = "red", "B" = "blue", "C" = "green", "D" = "purple", "E" = "orange")) +
  labs(color = "Category")

p