Format geom_text label doesn't work when using aes_string

问题:

I am using the dot function to format text labels in a plot created with ggplot2. This works fine when using aes, but doesn't work like expected when using aes_string. Is there a workaround to make it work with aes_string?

require(ggplot2)  # Define the format function dot <- function(x, ...) {    format(x, ..., big.mark = ".", scientific = FALSE, trim = TRUE) }  # Create dummy data df <- data.frame(cbind(levels(iris$Species),c(10000000000,200000,30000))) df$X2 <- as.numeric(as.character(df$X2))  # Works with aes    ggplot(iris) +    geom_bar(aes(Species,Sepal.Width),stat="identity") +        geom_text(data=df,aes(x=factor(X1),y=180,label=dot(X2)))   # Doesn't work with aes_string ggplot(iris) +    geom_bar(aes(Species,Sepal.Width),stat="identity") +   geom_text(data=df,aes_string(x="X1",y=180,label=dot("X2"))) 

回答1:

Rather than just quote "X2", you must quote the whole expression

ggplot(iris) +    geom_bar(aes(Species, Sepal.Width), stat = "identity") +    geom_text(data=df, aes_string(x="X1", y =180, label = "dot(X2)")) 

If you wanted to specify variable names via a character vector, you would use paste() to build that expression.

回答2:

You're passing a string constant to dot and dot("X2") returns "X2". So you're basically giving aes_string the argument label = "X2".

I got this to work

ggplot(iris) +    geom_bar(aes(Species, Sepal.Width), stat = "identity") +    geom_text(data=df, aes_string(x="X1", y =180, label = deparse(dot(df$X2)))) 

Edit

As suggested by MrFlick, you could also use df[,"X2"] if you need to pass the column name as a string. I.e.

ggplot(iris) +    geom_bar(aes(Species, Sepal.Width), stat = "identity") +    geom_text(data=df, aes_string(x="X1", y =180, label = deparse(dot(df[,"X2"])))) 

回答3:

As implied by my comment, I dislike relying on deparse or other evaluation tricks unless I have to:

col <- "X2" new_col <- paste0(col,"_dot") df[,new_col] <- dot(df[,col]) ggplot(iris) +      geom_bar(aes(Species,Sepal.Width),stat="identity") +      geom_text(data=df,aes_string(x="X1",y=180,label=new_col)) 

I presented this version as if we were writing code in a function and had received the "X2" as an argument.

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