ggplot标题部分斜体并换行显示的实现方法咨询

一、保留mdthemes，实现标题换行 #

mdthemes兼容HTML格式，直接用<br>标签替代\n即可实现换行，修改后的代码如下：

library(ggplot2)
library(mdthemes)

data(iris)
p <- ggplot(iris, aes(x=Species, y=Sepal.Length)) +     
  geom_boxplot(show.legend=FALSE, outlier.shape = NA, aes(fill = Species), alpha = 0.8) +               
  labs(title ="Sepal length (cm) of *setosa, versicolor, virginica* <br> exposed to different treatments") +
  theme_classic() +                                     
  theme(axis.title = element_text(face="bold"), 
        text = element_text(family = "serif", size = 12))
p + md_theme_classic() 

二、不依赖mdthemes，实现局部斜体+换行 #

如果不想使用mdthemes，有两种实用的替代方案：

1. 使用ggplot原生expression语法 #

通过italic()函数设置斜体，换行用\n，注意文本中的空格需要用~连接：

library(ggplot2)

data(iris)
p <- ggplot(iris, aes(x=Species, y=Sepal.Length)) +     
  geom_boxplot(show.legend=FALSE, outlier.shape = NA, aes(fill = Species), alpha = 0.8) +               
  labs(title = expression(Sepal~length~(cm)~of~italic(setosa, versicolor, virginica)~"\n"~exposed~to~different~treatments)) +
  theme_classic() +                                     
  theme(axis.title = element_text(face="bold"), 
        text = element_text(family = "serif", size = 12))
p

2. 使用ggtext包 #

ggtext支持解析markdown和HTML格式，只需将标题元素设置为element_markdown()，换行同样用<br>：

library(ggplot2)
library(ggtext)

data(iris)
p <- ggplot(iris, aes(x=Species, y=Sepal.Length)) +     
  geom_boxplot(show.legend=FALSE, outlier.shape = NA, aes(fill = Species), alpha = 0.8) +               
  labs(title ="Sepal length (cm) of *setosa, versicolor, virginica* <br> exposed to different treatments") +
  theme_classic() +                                     
  theme(axis.title = element_text(face="bold"), 
        text = element_text(family = "serif", size = 12),
        plot.title = element_markdown()) # 开启markdown解析
p

内容的提问来源于stack exchange，提问作者arnaudm