R语言ggplot双Y轴组合图中柱状图不显示的问题排查

问题背景 #

使用ggplot绘制包含柱状图与折线图的双Y轴组合图时，柱状图完全未显示。相关信息如下：

输入数据 #

reshaped_data <-
  structure(list(
    Year = c("2014", "2014", "2016", "2016", "2019", "2019", "2022", "2022"), 
    Total_percentage = c(0.23, 0.23, 0.21, 0.21, 0.21, 0.21, 0.18, 0.18), 
    Type = structure(c(2L, 1L, 2L, 1L, 2L, 1L, 2L, 1L), 
                     levels = c("Export", "Import"), class = "factor"), 
    Value = c(1020494000, 1334758000, 1243093000, 1734937000, 1551107000, 
              2155641000, 2257669000, 2433288000)), 
    row.names = c(NA, -8L), class = c("tbl_df", "tbl", "data.frame"))

原代码 #

ggplot(data = reshaped_data, aes(x = Year)) +
   geom_col(aes(y = Total_percentage, fill = "Total_percentage"), 
position = "dodge") +
   geom_line(aes(y = Value, color = Type, group = Type), size = 1) +
   geom_point(aes(y = Value, color = Type, group = Type), size = 3) +
   labs(
    title = "Total Percentage of Household Coffee Consumption against Coffee Trades in Malaysia From 2014 to 2022",
    x = "Year (2014-2022)",
    y = "Number of Trades (RM)"
  ) +
  coord_cartesian(ylim = c(0, 2500000000)) +
  scale_y_continuous(
    labels = scales::comma,
    breaks = seq(0, 2500000000, by = 500000000),
    sec.axis = sec_axis(
      trans = ~ (. / 1e9) * 10,  # Convert to percentage
      name = "Total Percentage of Household Coffee Consumption",
      labels = scales::percent_format(scale = 0.01)
    )
  ) +
  scale_fill_discrete(name = "Total Percentage of Household Coffee Consumption") +
  scale_color_manual(
    values = c("Import" = "#B2533E", "Export" = "#B5CB99"),
    name = "Type of Trades"
  )

效果对比 #

• 当前输出：仅显示折线图与散点，柱状图因数值过小完全不可见
• 预期输出：同时显示对应右侧百分比轴的柱状图，以及对应左侧贸易额轴的折线图

原因分析 #

1. 数值范围差距过大：柱状图的Total_percentage值在0.18-0.23之间，主Y轴范围却是0到25亿，数量级差达9个量级，导致柱状图被压缩成一条线。
2. 双Y轴转换逻辑倒置：副轴是将主Y轴数值转成百分比，但柱状图直接用原始百分比值映射主Y轴，未做反向转换，数值不在主Y轴可视范围内。

修正后的代码 #

library(ggplot2)
library(scales)

# 对年份的百分比数据去重，避免重复绘制重叠柱子
unique_perc <- reshaped_data[!duplicated(reshaped_data$Year), c("Year", "Total_percentage")]

ggplot() +
  # 柱状图：将百分比转换为主Y轴对应数值（副轴转换的逆运算）
  geom_col(data = unique_perc, 
           aes(x = Year, y = Total_percentage * 1e9 / 10, fill = "Total_percentage"), 
           width = 0.5) +
  # 折线图与散点图
  geom_line(data = reshaped_data, 
            aes(x = Year, y = Value, color = Type, group = Type), 
            size = 1) +
  geom_point(data = reshaped_data, 
             aes(x = Year, y = Value, color = Type, group = Type), 
             size = 3) +
  labs(
    title = "马来西亚家庭咖啡消费占比与咖啡贸易额对比（2014-2022）",
    x = "年份（2014-2022）",
    y = "贸易额（马币）"
  ) +
  coord_cartesian(ylim = c(0, 2500000000)) +
  scale_y_continuous(
    labels = comma,
    breaks = seq(0, 2500000000, by = 500000000),
    sec.axis = sec_axis(
      trans = ~ (. / 1e9) * 10,
      name = "家庭咖啡消费占比",
      labels = percent_format(scale = 0.01)
    )
  ) +
  scale_fill_manual(values = "#7F7F7F", 
                    name = "家庭咖啡消费占比") +
  scale_color_manual(
    values = c("Import" = "#B2533E", "Export" = "#B5CB99"),
    name = "贸易类型"
  ) +
  theme_minimal()

关键修正点 #

• 对百分比数据去重，每个年份仅保留一个值，避免重复绘制柱子导致重叠
• 将柱状图的y值按Total_percentage * 1e9 / 10转换，让百分比数值匹配主Y轴范围
• 优化标题与标签为中文，提升可读性
• 为柱状图指定填充色，避免默认配色冲突

内容的提问来源于stack exchange，提问作者Nur Husnina