如何不调整y值实现双Y轴叠加并保留ggplotly原始数据值

核心思路是利用双y轴实现不同量级数据的叠加展示，无需修改原始Balance数值，同时让ggplotly能正确显示原始数据。

代码示例 #

首先模拟一个贷款摊销数据集（你可以替换成自己的annual_amortization）：

# 模拟贷款摊销数据集
annual_amortization <- data.frame(
  Year = 1:10,
  Principal = c(8000, 8500, 9000, 9500, 10000, 10500, 11000, 11500, 12000, 12500),
  Interest = c(5000, 4500, 4000, 3500, 3000, 2500, 2000, 1500, 1000, 500),
  Balance = c(92000, 83500, 74500, 65000, 55000, 44500, 33500, 22000, 10000, 0)
)

接下来绘制带双y轴的ggplot并转换为ggplotly：

library(ggplot2)
library(plotly)

# 构建基础双y轴ggplot
p <- ggplot(annual_amortization, aes(x = Year)) +
  # 绘制Principal和Interest，对应左侧y轴
  geom_line(aes(y = Principal, color = "Principal"), linewidth = 1) +
  geom_line(aes(y = Interest, color = "Interest"), linewidth = 1) +
  # 将Balance映射到左侧y轴的数值范围（不修改原始数据）
  geom_line(aes(y = Balance / max(Balance) * max(c(Principal, Interest)), color = "Balance"), linewidth = 1) +
  # 设置双y轴：左侧显示Principal/Interest，右侧显示原始Balance
  scale_y_continuous(
    name = "Principal / Interest",
    sec.axis = sec_axis(
      trans = ~ . * max(annual_amortization$Balance) / max(c(annual_amortization$Principal, annual_amortization$Interest)),
      name = "Remaining Balance"
    )
  ) +
  scale_color_manual(values = c("Principal" = "blue", "Interest" = "red", "Balance" = "green")) +
  labs(title = "Loan Annual Amortization", x = "Year", color = "Category") +
  theme_minimal()

# 转换为ggplotly，确保tooltip显示原始数值
ggplotly(p, tooltip = c("x", "color")) %>%
  style(text = ~ifelse(color == "Balance", 
                       paste0("Balance: ", Balance),
                       paste0(color, ": ", y)))

关键说明 #

1. Balance数值映射：通过Balance / max(Balance) * max(c(Principal, Interest))将Balance的量级缩放到和Principal/Interest一致，实现折线叠加，但原始数据并未修改。
2. 双y轴转换：右侧y轴通过反向转换公式，把缩放后的数值还原为Balance的原始值，保证轴刻度显示真实剩余本金。
3. ggplotly tooltip处理：通过style函数判断折线类别，当为Balance时直接调用原始Balance字段展示，避免显示缩放后的数值。

内容的提问来源于stack exchange，提问作者Seoyoung Park