使用ggcorrplot在相关性矩阵上标注supertitle和index标签

我正在try 在使用ggcorrplot包创建的相关矩阵上自定义标签.然而，我无法让supertitle或subtitle格式发挥作用.如何在不使用Unicode字符的情况下让标签正确显示？

library(tidyverse)
library(ggcorrplot)

# Example Data
M <- cor(mtcars)[1:3,1:3]

# Attempt 1: Not formatted correctly
colnames(M) <- c("Temperature\n (^o C)", "PO[4]^2", "Oxygen\n (mg L^-1)")
rownames(M) <- c("Temperature\n (^o C)", "PO[4]^2", "Oxygen\n (mg L^-1)")

ggcorrplot(M,
           type = "lower",
           lab = TRUE,
           ggtheme = theme_bw())

# Attempt 2: Produces error message
ggcorrplot(M,
           type = "lower",
           lab = TRUE,
           scale_x_discrete(labels = c("mpg" = expression(Temperature~(degree*C)),
                                       "cyl" = expression(PO[4]^2),
                                       "disp" = expression(Oxygen~(mg~L^-1)))),
           scale_y_discrete(labels = c("mpg" = expression(Temperature~(degree*C)),
                                       "cyl" = expression(PO[4]^2),
                                       "disp" = expression(Oxygen~(mg~L^-1)))),
           ggtheme = theme_bw())
#> Error in match.arg(method): 'arg' must be NULL or a character vector

^{创建于2024年4月23日，共有reprex v2.1.0个}