geom_label_repel未关联sec.axis求助：双轴ggplot标签无法自动定位

问题核心是标签的Y轴映射未和折线保持一致：你的折线通过prop*15将次轴数值缩放到主轴范围，但标签用的是prop*1，导致位置完全偏离折线。

修正步骤 #

• 将geom_label_repel中的y = prop*1改为y = prop*15，和折线的Y轴缩放系数统一
• 修正arrange的错误写法（原代码arrange(df, by = day)简化为arrange(day)）
• 调整次轴breaks参数（原范围0-10超出次轴实际值，改为0-1匹配prop的取值范围）

完整修正代码 #

library(ggplot2)
library(dplyr)
library(scales)

df <- data.frame(day = as.character(seq(from = 1, to = 100, by = 1)),
                 total = rbinom(n=100,30,0.5), 
                 prop = runif(100))

df <- df %>% arrange(day)
df$`percentage` <- label_percent(accuracy = 0.01)(df$prop)


ggplot(data = df, 
       aes(x = day, y = total)) +
  geom_bar(stat = "identity", fill = "lightgreen", width = 0.35) + 
  geom_line(aes(x = day, y = prop*15, group = 1), 
            color = "red", size = 1) +
  scale_y_continuous( 
    labels = function(x) format(x, scientific = FALSE),
    sec.axis = sec_axis(trans = ~./15, 
                        name = "Secondary axis",
                        breaks = seq(from = 0, to = 1, by = 0.1),
                        labels = scales::percent))+
  theme(axis.text.x = element_text(angle = 90, vjust = 0.5))+
  geom_label_repel(data=df[nrow(df),], 
                   aes(x = day, 
                       y = prop*15,
                       label = paste0(round(prop*100,2), "%")),
                   color = 'red',
                   segment.alpha = 0.5) +
  scale_x_discrete(expand = expansion(add = c(0, 7)))

关键说明 #

• 双轴图表本质是将次轴数据缩放后映射到主轴，所有关联次轴的图层（折线、标签）必须使用相同的缩放比例
• sec_axis的breaks要匹配转换后的数据范围，避免出现无效刻度
• 标签文本追加%符号，和次轴的百分比格式保持一致，提升可读性

内容的提问来源于stack exchange，提问作者Bileobio