如何在R中为两个拼接的分面图添加右侧Y轴标签？

方法1：为每个子图添加独立的右侧Y轴标签 #

这种方法通过scale_y_continuous()的sec.axis参数配合主题设置，让每个子图的右侧显示对应Y轴标签，适合上下图需要不同标签的场景。

library(ggplot2)
library(patchwork)

# 第一个数据集与绘图
data_sample <- data.frame(
  group = rep(c("A", "B"), each = 20),
  n_classes = rep(c("xyz", "zyx"), each = 10),
  indicator = rep(c("Indicator 1", "Indicator 2"), each = 20),
  ICC = runif(40, 0, 1),
  extrapolation_rate = runif(40, 0, 1)
)

basic_facet_plot1 <- ggplot(data_sample, aes(x = ICC, y = extrapolation_rate, color = group)) +
  geom_point() +
  facet_grid(indicator ~ n_classes) +
  theme_minimal() +
  labs(title = "Sample Facet Plot", y = "Something", color = "Group") +
  theme(axis.title.x = element_blank()) +
  # 添加右侧Y轴并配置标签
  scale_y_continuous(sec.axis = dup_axis(name = "Something")) +
  theme(
    axis.title.y.right = element_text(angle = 90, margin = margin(l = 15)),
    axis.ticks.y.right = element_blank(),  # 可选：隐藏右侧刻度线
    axis.text.y.right = element_blank()    # 可选：隐藏右侧刻度文本
  )

# 第二个数据集与绘图
data_sample <- data.frame(
  group = rep(c("A", "B"), each = 20),
  n_classes = rep(c("abc", "cba"), each = 10),
  indicator = rep(c("Indicator 3", "Indicator 4"), each = 20),
  ICC = runif(40, 0, 1),
  extrapolation_rate = runif(40, 0, 1)
)

basic_facet_plot2 <- ggplot(data_sample, aes(x = ICC, y = extrapolation_rate, color = group)) +
  geom_point() +
  facet_grid(indicator ~ n_classes) +
  theme_minimal() +
  labs(y = "Something else", color = "Group", x = "ICC") +
  # 添加右侧Y轴并配置标签
  scale_y_continuous(sec.axis = dup_axis(name = "Something else")) +
  theme(
    axis.title.y.right = element_text(angle = 90, margin = margin(l = 15)),
    axis.ticks.y.right = element_blank(),
    axis.text.y.right = element_blank()
  )

# 调整边距并拼接
basic_facet_plot1 <- basic_facet_plot1 + theme(plot.margin = margin(t = 1, r = 1, b = -2, l = 1, unit = "cm"))
basic_facet_plot2 <- basic_facet_plot2 + theme(plot.margin = margin(t = 0, r = 1, b = 0, l = 1, unit = "cm"))

combined_plot <- basic_facet_plot1 / basic_facet_plot2
final_plot <- combined_plot + plot_layout(guides = 'collect') & theme(legend.position = 'bottom')

print(final_plot)

方法2：添加全局右侧Y轴标签 #

如果需要一个统一的右侧标签，可借助grid包创建文本对象，配合patchwork布局将标签添加到拼接图右侧。

library(ggplot2)
library(patchwork)
library(grid)

# 原始子图代码（保持原有逻辑）
data_sample <- data.frame(
  group = rep(c("A", "B"), each = 20),
  n_classes = rep(c("xyz", "zyx"), each = 10),
  indicator = rep(c("Indicator 1", "Indicator 2"), each = 20),
  ICC = runif(40, 0, 1),
  extrapolation_rate = runif(40, 0, 1)
)

basic_facet_plot1 <- ggplot(data_sample, aes(x = ICC, y = extrapolation_rate, color = group)) +
  geom_point() +
  facet_grid(indicator ~ n_classes) +
  theme_minimal() +
  labs(title = "Sample Facet Plot", y = "Something", color = "Group") +
  theme(axis.title.x = element_blank())

data_sample <- data.frame(
  group = rep(c("A", "B"), each = 20),
  n_classes = rep(c("abc", "cba"), each = 10),
  indicator = rep(c("Indicator 3", "Indicator 4"), each = 20),
  ICC = runif(40, 0, 1),
  extrapolation_rate = runif(40, 0, 1)
)

basic_facet_plot2 <- ggplot(data_sample, aes(x = ICC, y = extrapolation_rate, color = group)) +
  geom_point() +
  facet_grid(indicator ~ n_classes) +
  theme_minimal() +
  labs(y = "Something else", color = "Group", x = "ICC")

# 调整边距（缩小右侧边距避免空白）
basic_facet_plot1 <- basic_facet_plot1 + theme(plot.margin = margin(t = 1, r = 0, b = -2, l = 1, unit = "cm"))
basic_facet_plot2 <- basic_facet_plot2 + theme(plot.margin = margin(t = 0, r = 0, b = 0, l = 1, unit = "cm"))

# 创建全局右侧Y轴标签
right_y_label <- textGrob("全局Y轴标签", rot = 90, gp = gpar(fontsize = 12, fontface = "bold"))

# 创建空白占位图放置标签
spacer <- plot_spacer() + 
  theme_void() + 
  annotation_custom(right_y_label, xmin=0, xmax=1, ymin=0, ymax=1)

# 拼接布局：左侧为上下子图，右侧为标签区域
combined_plot <- (basic_facet_plot1 / basic_facet_plot2) | spacer +
  plot_layout(widths = c(25, 1)) # 调整宽度比例，控制标签区域宽度

# 整理图例
final_plot <- combined_plot + plot_layout(guides = 'collect') & theme(legend.position = 'bottom')

print(final_plot)

内容的提问来源于stack exchange，提问作者Linus