向ggplot2中的实验室传递字符串变量不被接受

Question

seed=1234
df=data.frame(rnorm(50)*100)
names(df)="Temperature"; df
nn = length(df$Temperature)
title = "Daily Temperature"
title2 = substitute(paste(title,"(",degree,"C)"))
title3 = paste(title,"\n(n = ",nn,")")
h1 = ggplot(df, aes(x=df[,1]))+ geom_density(colour = "black", fill = "white", binwidth = 5)
+    labs(list(title = title3, x = title2, y = "Counts"))
h1

上面的小例子描述了我在x轴上显示"title2“的问题。我搜索并尝试了许多好的建议(例如，aes_string、表达式等)。但还是不能让这件事起作用。如果我将title2替换为；title2 = expression(paste("Daily Temperature (",degree,"C)"))，它可以正常工作。提前感谢您的帮助！文斯

Answer 1

require(ggplot2)  # not everyone has this package loaded by default
seed=1234
df=data.frame(rnorm(50)*100)
names(df)="Temperature"; df
nn = length(df$Temperature)
title = "Daily Temperature"

要做到这一点，就需要有算计的经验。看到了吗?计谋和?替代。我发现，如果您使用paste和*，那么通常不需要使用图形化的~。

  # first argument to substitute is an expression object
  # you need to supply a list as the second argument to substitute 
title2 = substitute(title*"("*degree*C*")", list(title=title) )
title3 = paste(title,"\n(n = ",nn,")")
h1 = ggplot(df, aes(x=df[,1]))+ 
  geom_density(colour = "black", fill = "white", binwidth = 5) + 
  labs(list(title = title3, x = title2, y = "Counts"))
h1

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另一种在绘图表达式中使用圆括号的方法是使用plotmath函数(它不同于普通的list函数，因为它创建逗号分隔的表达式)。只有一个表达式，它只给出括号：

title2 = substitute(title*list(degree*C), list(title=title) )