如何让ggh4x::facet_nested()面板宽高随文本自适应或手动设置？

ggh4x的facet_nested()默认的space="free_y"是根据面板的坐标轴范围分配空间，而非分面文本的长度，所以会出现所有面板宽度一致的情况。以下两种方法可以实现面板宽度随文本自适应或手动指定：

方法1：手动指定嵌套层级的面板宽度 #

通过提取ggplot生成的gtable对象，直接修改对应分面strip和面板的宽度参数，适合需要精确控制空间的场景：

library(ggplot2)
library(ggh4x)
library(dplyr)
library(gtable)
library(grid)

# 生成数据并创建绘图对象
p <- data.frame(
  top1 = sample(c(1, 2, 3), size = 1000, replace = TRUE),
  left1 = sample(c("a", "b", "c"), size = 1000, replace = TRUE),
  left2 = sample(
    c("A medium text", "An even longer text\nwith several rows\nfoo"),
    size = 1000, replace = TRUE
  ),
  left3 = sample(c("d", "e", "f"), size = 1000, replace = TRUE),
  value = rnorm(1000)
) |>
  group_by(top1, left1, left2, left3) |>
  summarise(value = mean(value), .groups = "drop") |>
  ggplot() +
  ggh4x::facet_nested(
    left1 + left2 + left3 ~ top1,
    switch = "y", scales = "free",
    drop = TRUE, space = "free_y"
  ) +
  geom_tile(aes(x = 0, y = 0, fill = value)) +
  theme(
    axis.title = element_blank(),
    axis.ticks = element_blank(),
    axis.text = element_blank(),
    strip.text.y.left = element_text(angle = 0),
    strip.background.y = element_rect(fill = "grey90", colour = "grey10")
  )

# 提取底层gtable对象
gt <- ggplotGrob(p)

# 定位左侧分面strip和面板的列索引
strip_y_cols <- which(grepl("strip-l", gt$layout$name))
panel_cols <- which(grepl("panel", gt$layout$name))

# 手动设置宽度（单位：cm），可根据文本长度调整数值
gt$widths[strip_y_cols] <- unit(c(2, 5, 2), "cm")
gt$widths[panel_cols] <- unit(c(3, 3, 3), "cm") # 可选：调整面板本身宽度

# 绘制调整后的图形
grid.draw(gt)

方法2：基于文本长度自动计算宽度 #

通过测量每个分面文本的实际宽度，自动调整strip和面板的空间，实现真正的自适应：

library(ggplot2)
library(ggh4x)
library(dplyr)
library(gtable)
library(grid)

# 生成数据并创建绘图对象
p <- data.frame(
  top1 = sample(c(1, 2, 3), size = 1000, replace = TRUE),
  left1 = sample(c("a", "b", "c"), size = 1000, replace = TRUE),
  left2 = sample(
    c("A medium text", "An even longer text\nwith several rows\nfoo"),
    size = 1000, replace = TRUE
  ),
  left3 = sample(c("d", "e", "f"), size = 1000, replace = TRUE),
  value = rnorm(1000)
) |>
  group_by(top1, left1, left2, left3) |>
  summarise(value = mean(value), .groups = "drop") |>
  ggplot() +
  ggh4x::facet_nested(
    left1 + left2 + left3 ~ top1,
    switch = "y", scales = "free",
    drop = TRUE, space = "free_y"
  ) +
  geom_tile(aes(x = 0, y = 0, fill = value)) +
  theme(
    axis.title = element_blank(),
    axis.ticks = element_blank(),
    axis.text = element_blank(),
    strip.text.y.left = element_text(angle = 0),
    strip.background.y = element_rect(fill = "grey90", colour = "grey10")
  )

# 提取底层gtable对象
gt <- ggplotGrob(p)

# 获取所有左侧分面的文本内容
strip_elements <- gt$grobs[grepl("strip-l", gt$layout$name)]
strip_texts <- lapply(strip_elements, function(x) x$grobs[[1]]$children[[1]]$label)

# 测量每个文本的实际宽度（匹配当前主题字体）
text_widths <- sapply(strip_texts, function(txt) {
  grob <- textGrob(txt, gp = getThemeElement("strip.text.y.left")$gp)
  convertWidth(grobWidth(grob), "cm", valueOnly = TRUE)
})

# 添加边距后设置strip宽度
adjusted_strip_widths <- unit(text_widths + 0.5, "cm")
strip_y_cols <- which(grepl("strip-l", gt$layout$name))
gt$widths[strip_y_cols] <- adjusted_strip_widths

# 可选：同步调整面板宽度
# panel_cols <- which(grepl("panel", gt$layout$name))
# gt$widths[panel_cols] <- unit(rep(3, length(panel_cols)), "cm")

# 绘制调整后的图形
grid.draw(gt)

注意事项 #

• 两种方法都依赖gtable和grid包操作底层绘图对象
• 多层嵌套分面时，需要通过gt$layout查看元素位置，精准匹配strip和面板的对应关系
• 若需要调整y轴方向的面板高度，只需将代码中的widths替换为heights，对应调整行索引即可

内容的提问来源于stack exchange，提问作者Léa