将字符串变量传递给ggplot2中的实验室不被接受

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

上面的迷你示例描述了我在x轴上显示“title2”的问题。我已经搜索并尝试了许多好的建议（例如，aes_string，expression等等），但仍然无法使其工作。如果我用title2替换title2; title2 = expression(paste("Daily Temperature (",degree,"C)"))，它运作正常。在此先感谢您的帮助！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"

要干净利落地完成这项工作需要积累经验。参见？plotmath和？substitute。我发现如果您使用paste和*，通常不需要使用plotmath ~。

  # 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

在plotmath表达式中使用括号的另一种方法是使用plotmath list函数（这与普通列表函数的不同之处在于它创建了逗号分隔的表达式。）只有一个表达式，它只是给出了括号：

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