如何在ggplot制作的barplot中标注阈值线下？

library(ggplot2)

# 创建数据框
data <- data.frame(category = c("A", "B", "C", "D"),
                   value = c(10, 20, 15, 25))

# 创建基本的barplot图形
p <- ggplot(data, aes(x = category, y = value)) +
  geom_bar(stat = "identity")

# 添加阈值线
threshold <- 18
p <- p + geom_hline(yintercept = threshold, linetype = "dashed", color = "red")

# 添加文本标注
label <- "Threshold"
p <- p + geom_text(x = 0.5, y = threshold, label = label, vjust = -0.5, color = "red")

library(ggplot2)

# 创建数据框
data <- data.frame(category = c("A", "B", "C", "D"),
                   value = c(10, 20, 15, 25))

# 创建基本的barplot图形
p <- ggplot(data, aes(x = category, y = value)) +
  geom_bar(stat = "identity")

# 添加阈值线
threshold <- 18
p <- p + geom_hline(yintercept = threshold, linetype = "dashed", color = "red")

# 添加文本标注
label <- "Threshold"
p <- p + geom_text(x = 0.5, y = threshold, label = label, vjust = -0.5, color = "red")

# 显示图形
print(p)