R ggplot2绘制水平点图如何添加右侧次坐标轴映射第三个变量

在R中使用ggplot2绘制水平点图时，数据集包含3个数值型变量与1个分类变量，当前已完成映射：

• 分类变量origin映射到y轴
• 数值变量change、rate以带数值标注的圆点形式在主x轴展示
• 需要将第三个数值变量Percentage映射到图右侧，对齐每个分类行展示对应数值，添加次坐标轴标注。

原始可复现代码如下：

df <- data.frame (origin = c("A","B","C","D","E","F","G","H","I","J"),
                  Percentage = c(23,16,32,71,3,60,15,21,44,60),
                  rate = c(10,12,20,200,-25,12,13,90,-105,23),
                  change = c(10,12,-5,12,6,8,0.5,-2,5,-2))

library(ggplot2)

ggplot(df, aes(x = rate, y = factor(origin, rev(origin)))) +
  geom_hline(aes(yintercept = origin), color = 'gray') +
  geom_vline(xintercept = 0, linetype = 2, color = 'gray') +
  geom_point(aes(color = 'Rate'), size = 10) +
  geom_text(aes(label = rate), color = 'white') +
  geom_point(aes(x = change, color = 'Change'), size = 10) +
  geom_text(aes(label = change, x = change)) +
  theme_minimal(base_size = 16) +
  scale_x_continuous(labels = ~paste0(.x, '%'), name = NULL) +
  scale_color_manual(values = c('#aac7c4', '#5f9299')) +
  theme(panel.grid = element_blank(),
        axis.text.y = element_text(color = 'gray50')) +
  labs(color = NULL, y = NULL)

当前输出效果：

预期输出效果：

ggplot2次坐标轴需要和主轴满足线性映射关系，分类y轴无法直接关联数值次轴，按以下步骤修改即可：

• 先把分类y轴转为数值位置索引，保留原有分类排序，主y轴刻度仍展示原分类标签
• 扩展主x轴右侧范围，预留Percentage数值的展示空间
• 在x轴最右侧的固定位置，对齐每个分类的y坐标添加Percentage文本标注
• 添加右侧次y轴，仅保留"Percentage"标题作为列说明，隐藏多余刻度

修改后的完整代码：

df <- data.frame (origin = c("A","B","C","D","E","F","G","H","I","J"),
                  Percentage = c(23,16,32,71,3,60,15,21,44,60),
                  rate = c(10,12,20,200,-25,12,13,90,-105,23),
                  change = c(10,12,-5,12,6,8,0.5,-2,5,-2))

library(ggplot2)

# 计算y轴位置索引，保持原有分类排序
df$y_pos <- match(df$origin, rev(df$origin))

ggplot(df, aes(x = rate, y = y_pos)) +
  geom_hline(aes(yintercept = y_pos), color = 'gray') +
  geom_vline(xintercept = 0, linetype = 2, color = 'gray') +
  geom_point(aes(color = 'Rate'), size = 10) +
  geom_text(aes(label = rate), color = 'white') +
  geom_point(aes(x = change, color = 'Change'), size = 10) +
  geom_text(aes(label = change, x = change)) +
  # 右侧添加Percentage数值标注
  geom_text(aes(x = 220, label = paste0(Percentage, "%")), size = 5, color = "gray30") +
  theme_minimal(base_size = 16) +
  scale_x_continuous(
    labels = ~paste0(.x, '%'), 
    name = NULL, 
    # 扩展x轴范围，左侧留边距、右侧留标注空间
    limits = c(-120, 240)
  ) +
  scale_y_continuous(
    breaks = 1:10,
    labels = rev(df$origin),
    name = NULL,
    # 添加右侧次坐标轴，仅显示标题
    sec.axis = sec_axis(~., name = "Percentage", breaks = NULL, labels = NULL)
  ) +
  scale_color_manual(values = c('#aac7c4', '#5f9299')) +
  theme(
    panel.grid = element_blank(),
    axis.text.y = element_text(color = 'gray50'),
    # 调整右侧次轴标题为横向，放在右上角位置
    axis.title.y.right = element_text(angle = 0, vjust = 1.02, hjust = 0, margin = margin(l = 8))
  ) +
  labs(color = NULL)

运行代码后即可得到和预期一致的输出效果，右侧对齐展示每个分类对应的Percentage数值，次轴标题清晰说明列含义，原有图表元素完全保留。

内容的提问来源于stack exchange，提问作者user18948933