如何在一个方面标签中包含希腊符号？

Question

我正在尝试使用ggplot2（v。2_2.2.1）创建一个图facet_wrap，并且我只需要在一个构面标签（五个之中）中具有希腊符号。我试图使用这里在堆栈溢出中发布的代码：

• R刻面网格中的R希腊字母和刻面标签的普通字母
• 如何在facet_wrap中的标签上添加表达式？
• 如何使用网格编辑ggplot2对象以将数学表达式添加到构面标签？

但没有成功（getGrob无法正常工作，对于mf_labeller也是如此）。

有人可以帮我吗？

这是示例代码：

df <- data.frame(genes = rep(c("BA","MLL","pos","neg","PMLalpha+"),5), value = sample(1:100, 25, replace=TRUE))
df$genes <- factor(df$genes, levels = c("BA","MLL","pos","neg","PMLalpha+"), ordered = TRUE)
ggplot(df,aes(x=genes, y=value)) + geom_boxplot()+ 
  facet_wrap(~genes, ncol = 5,scales = "free_x")+
  scale_x_discrete(name="",
               breaks = c("BA","MLL","pos","neg","PMLalpha+"),
               labels = c("BA","MLL","pos","neg",expression(paste("PML", alpha,"+"))))

我能够重命名x轴刻度线，但是我无法在构面标签中执行此操作。

Answer 1

这是使用的技巧labeller=label_parsed。

首先，定义df$genes使用要解析的表达式的标签：

df$genes <- factor(df$genes, levels = c("BA","MLL","pos","neg","PMLalpha+"),
 ordered = TRUE, labels=c("BA","MLL","pos","neg",expression(paste("PML", alpha,"+"))))

然后使用labeller=label_parsed在facet_wrap：

ggplot(df,aes(x=genes, y=value)) + geom_boxplot()+ 
  facet_wrap(~genes, ncol = 5, scales = "free_x", labeller = label_parsed)

如您所见，这与x轴标签混为一谈，但是您可以scale_x_discrete按以下步骤进行修复：

ggplot(df,aes(x=genes, y=value)) + geom_boxplot()+ 
  facet_wrap(~genes, ncol = 5, scales = "free_x", labeller = label_parsed) +
  scale_x_discrete(name="",
               breaks = c("BA","MLL","pos","neg","paste(\"PML\", alpha, \"+\")"),
               labels = c("BA","MLL","pos","neg", expression(paste("PML", alpha,"+"))))