Get the unquoted value of a string variable inside of aes() call

Question

I would like to generate a hovertext for ggplotly() using aes() along the lines of

mapping <- aes(text = paste0(
    "Value: ",
    columnName
))

where columnName is a variable containing a column name as a string. Now, I don't want columnName recognized as a column name itself. If columnName == "col1" the result I want is

aes(text = paste0(
   "Value: ",
    col1
))

which evaluates to the aesthetic mapping `text` -> `paste0("Value: ", col1)`.

I have tried using aes_string(), but

columnName <- "col1"
aes_string(text = paste0(
    "Value: ",
    columnName
))

just evaluates to the aesthetic mapping `x` -> `Value:col1`.

How do I make this work?

Answer 1

Apparently OP wants to create an expression object in order to evaluate it later on. That can be achieved using bquote (or substitute or some function from the tidyverse wich probably involves exclamation marks):

columnName <- "col1"
columnName <- as.name(columnName) #first turn the character string into a quoted name
mapping <- bquote(aes(text = paste0(
  "Value: ",
  .(columnName) #this substitutes the name into the expression
))
)
#aes(text = paste0("Value: ", col1))