R中地图饼图中不同字符串的特定不同颜色

install.packages("ggplot2")
install.packages("maps")

library(ggplot2)
library(maps)

data <- data.frame(region = c("Asia", "Europe", "North America"),
                   category = c("Category A", "Category B", "Category C"))

world_map <- map_data("world")

merged_data <- merge(world_map, data, by.x = "region", by.y = "region", all.x = TRUE)

ggplot(merged_data, aes(x = long, y = lat, group = group, fill = category)) +
  geom_polygon() +
  coord_equal() +
  scale_fill_manual(values = c("Category A" = "red", "Category B" = "blue", "Category C" = "green")) +
  theme_void()