轴文本 ggplot2 中的下标

Question

我对 R 比较陌生，作为一名化学家，我需要经常使用下标。特别是，例如在这张图中：

我使用的代码如下：

ggline(my_data, x = "ATPS", y = "PRYBSA", color = "Pretreatment",
       add = "mean_sd", size=1, ylim=c(0,105),
       palette = c("#00AFBB", "#E7B800"), legend="right",
       ylab ="Protein recovery yield / %",error.plot = "errorbar") + theme(axis.text=element_text(size=20), axis.title=element_text(size=24,face="bold"), legend.title=element_text(size=24),legend.text=element_text(size=22))
TukeyHSD(prybsa.aov, which = "ATPS")

变量“ATPS”有三个水平：Bet:2LA/K2HPO4, ChCl:2Urea/K2HPO4 和 ChCl:2Urea/K3PO4，但我希望它们以下标出现 Bet:2LA/K₂HPO₄, ChCl :2Urea/K₂HPO₄ 和 ChCl:2Urea/K₃PO₄.

Answer 1

实现您想要的结果的一个选择是使用

recode

符号添加下标

?plotmath

您的标签。然后使用例如

scales::label_parse

在

scale_x_discrete

解析数学表达式：

使用一些虚假的随机示例数据：

set.seed(123)

my_data <- data.frame(
  ATPS = rep(c("Bet:2LA/K2HPO4", "ChCl:2Urea/K2HPO4", "ChCl:2Urea/K3PO4"), each = 2),
  Pretreatment = c("Mortar", "None"),
  PRYBSA = runif(10 * 6, 0, 100)
)

library(ggpubr)
#> Loading required package: ggplot2

my_data$ATPS <- dplyr::recode(
  my_data$ATPS,
  "Bet:2LA/K2HPO4" = "Bet:2*LA/K[2]*HPO[4]",
  "ChCl:2Urea/K2HPO4" = "ChCl:2*Urea/K[2]*HPO[4]",
  "ChCl:2Urea/K3PO4" = "ChCl:2*Urea/K[3]*PO[4]"
)

ggline(my_data,
  x = "ATPS", y = "PRYBSA", color = "Pretreatment",
  add = "mean_sd", size = 1, ylim = c(0, 105),
  palette = c("#00AFBB", "#E7B800"),
  legend = "right",
  ylab = "Protein recovery yield / %",
  error.plot = "errorbar"
) + 
  scale_x_discrete(labels = scales::label_parse())

第二种也许更轻量级的方法是使用Unicode下标：

my_data$ATPS <- dplyr::recode(
  my_data$ATPS,
  "Bet:2LA/K2HPO4" = "Bet:2LA/K\u2082HPO\u2084",
  "ChCl:2Urea/K2HPO4" = "ChCl:2Urea/K\u2082HPO\u2084",
  "ChCl:2Urea/K3PO4" = "ChCl:2Urea/K\u2083*PO\u2084"
)

ggline(my_data,
       x = "ATPS", y = "PRYBSA", color = "Pretreatment",
       add = "mean_sd", size = 1, ylim = c(0, 105),
       palette = c("#00AFBB", "#E7B800"),
       legend = "right",
       ylab = "Protein recovery yield / %",
       error.plot = "errorbar"
)