使用ggplot2在堆叠条形图上显示透明图层

library(ggplot2)

# 创建示例数据
data <- data.frame(
  category = c("A", "B", "C"),
  value1 = c(20, 30, 40),
  value2 = c(10, 15, 25)
)

# 绘制堆叠条形图
plot <- ggplot(data, aes(x = category)) +
  geom_bar(aes(y = value1, fill = "Value 1"), stat = "identity") +
  geom_bar(aes(y = value2, fill = "Value 2"), stat = "identity") +
  scale_fill_manual(values = c("Value 1" = "blue", "Value 2" = "red")) +
  labs(x = "Category", y = "Value", title = "Stacked Bar Chart")

# 添加透明图层
plot <- plot +
  geom_rect(aes(xmin = -Inf, xmax = Inf, ymin = -Inf, ymax = Inf),
            fill = "black", alpha = 0.2)

# 显示图形
print(plot)