如何在ggplot分面标题中拼接变量并实现换行与部分加粗

要实现分面标题换行、上半部分加粗且字号更大的效果，你需要用plotmath的atop()函数实现换行，结合bold()和字号控制函数（如huge()/large()）设置格式，同时在mutate中逐行生成符合plotmath语法的字符串，最后用label_parsed解析。

方法1：直接构造Plotmath字符串 #

这种方法通过sprintf和map2_chr逐行生成可解析的plotmath字符串，代码简洁直观：

library(ggplot2)
library(dplyr)
library(purrr)

mpg_df <- mpg %>%
  select(year, manufacturer, model, cty, hwy) %>%
  filter(
    (year == 1999 & manufacturer == "audi" & model == "a4 quattro") |
      (year == 2008 & manufacturer == "dodge" & model == "ram 1500 pickup 4wd")
  ) %>%
  # 逐行生成带格式的plotmath字符串
  mutate(title = map2_chr(manufacturer, model, ~ {
    sprintf(
      "atop(bold(huge('This is the manufacturer %s')), 'This is the model %s')",
      .x, .y
    )
  }))

# 绘制图形
mpg_df %>%
  ggplot(aes(x = cty, y = hwy)) +
  geom_point() +
  facet_wrap(~ title, labeller = label_parsed) +
  theme_classic()

方法2：用bquote生成表达式再转字符串 #

如果更习惯用bquote嵌入变量，需要结合rowwise()逐行处理，再用deparse()把表达式转成字符串：

library(ggplot2)
library(dplyr)

mpg_df <- mpg %>%
  select(year, manufacturer, model, cty, hwy) %>%
  filter(
    (year == 1999 & manufacturer == "audi" & model == "a4 quattro") |
      (year == 2008 & manufacturer == "dodge" & model == "ram 1500 pickup 4wd")
  ) %>%
  rowwise() %>%
  mutate(title = deparse(bquote(
    atop(bold(huge("This is the manufacturer " * .(manufacturer))),
         "This is the model " * .(model))
  ))) %>%
  ungroup()

# 绘制图形
mpg_df %>%
  ggplot(aes(x = cty, y = hwy)) +
  geom_point() +
  facet_wrap(~ title, labeller = label_parsed) +
  theme_classic()

关键说明 #

• 之前用\n换行无效：plotmath不识别文本换行符，必须用atop()实现上下分行。
• 字号控制：plotmath提供huge()/large()/small()等函数调整字号，按需替换即可。
• 变量嵌入：无论是sprintf还是bquote，核心是把动态变量正确嵌入到plotmath语法中，确保label_parsed能解析。

内容的提问来源于stack exchange，提问作者AndrewGB