如何在R语言帕累托图中基于次Y轴80%值添加截线

需求说明 #

已完成帕累托图主体绘制，需添加两条红色虚线：

• 在右侧次Y轴80%位置绘制水平红线，与累积频率曲线相交
• 从交点向下绘制垂直线至X轴

修改后的完整代码 #

defect <- c(80, 27, 66, 94, 33, 354, 32, 77, 567) 
names(defect) <- c("Jafar", "Ali", "Mamal", "Mosi", "Hamed", "Haney", "Munny", "Funny", "Foony")

d <- data.frame(defect) 

# 修正：将行名转为category列，避免绘图报错
d <- d %>%
  mutate(category = rownames(.)) %>%
  arrange(desc(defect)) %>%
  mutate(
    cumsum = cumsum(defect),
    freq = round(defect / sum(defect), 3),
    cum_freq = cumsum(freq)
  )

## 保存默认绘图参数
def_par <- par() 

# 设置新边距
par(mar=c(5,5,4,5)) 

## 绘制条形图，pc存储条形的x坐标
pc <- barplot(d$freq,
             width = 1, space = 0.2, border = NA, axes = F,
             ylim = c(0, 1.05 * max(d$freq, na.rm = T)), 
             ylab = "相对频率" , cex.names = 0.7, 
             names.arg = d$category,
             main = "帕累托图")

## 标注左侧Y轴
axis(side = 2, at = c(0, d$freq), las = 1, col.axis = "grey62", col = "grey62", tick = T, cex.axis = 0.8)

## 添加图框
box(col = "grey62")

## 绘制累积频率曲线
max_freq <- max(d$freq, na.rm = T)
px <- d$cum_freq * max_freq
lines(pc, px, type = "b", cex = 0.7, pch = 19, col="cyan4")

## 添加右侧Y轴
axis(side = 4, at = seq(0, max_freq, length.out = 5), 
     labels = paste(seq(0, 100, 25), "%", sep=""), 
     las = 1, col.axis = "cyan4", col = "cyan4", cex.axis = 0.8)

## 绘制80%红线
# 计算80%对应的左侧Y轴数值
y_80 <- 0.8 * max_freq
# 找到第一个累积频率≥80%的条形位置
idx <- which(d$cum_freq >= 0.8)[1]
x_pos <- pc[idx]

# 水平红色虚线
abline(h = y_80, col = "red", lty = 2)
# 垂直红色虚线
abline(v = x_pos, col = "red", lty = 2)

## 恢复默认绘图参数
par(def_par)

关键修改说明 #

1. 修正标签列：原代码中names.arg = d$category会报错，这里将行名转为category列，确保条形图标签正常显示。
2. 优化右侧Y轴：改为生成均匀刻度（0%、25%、50%、75%、100%），视觉更规范。
3. 红线绘制逻辑：
   • 映射80%累积频率到左侧Y轴刻度：y_80 = 0.8 * max(d$freq)
   • 定位第一个达到80%累积频率的条形X坐标
   • 用abline()绘制水平/垂直红色虚线（lty=2代表虚线样式）

内容的提问来源于stack exchange，提问作者Oscar