Turn a {{}} (dplyr double curly braces) interpolation into a string

Question

Let's assume I have the following R function:

library(tidyverse)

f <- function(.df, .var) {
  .df %>% ggplot(aes(x = wt, y = {{ .var }})) +
    geom_point() +
    ggtitle({{ .var }})
}

f(mtcars, hp)
#> Error in list2(..., title = title, subtitle = subtitle, caption = caption, : object 'hp' not found
f(mtcars, qsec)
#> Error in list2(..., title = title, subtitle = subtitle, caption = caption, : object 'qsec' not found

^{Created on 2021-01-08 by the reprex package (v0.3.0)}

How do I access the actual string that .var takes to use when creating a title?

score 1 · Accepted Answer · answered Jan 08 '21 at 11:07

Instead of the double curly braces, which evaluate the variable in context of the data frame, you need to use enquo to get a string:

library(tidyverse)

f <- function(.df, .var) {
  .df %>% ggplot(aes(x = wt, y = {{ .var }})) +
    geom_point() +
    ggtitle(enquo(.var))
}

f(mtcars, hp)

^{Created on 2021-01-08 by the reprex package (v0.3.0)}

score 1 · Answer 2 · answered Jan 08 '21 at 14:31

1

You can use deparse + substitute to change unquoted value to a string which can be used in ggtitle.

library(ggplot2)

f <- function(.df, .var) {
  title <- deparse(substitute(.var))
  
  .df %>% ggplot(aes(x = wt, y = {{ .var }})) +
    geom_point() +
    ggtitle(title)
}

f(mtcars, hp)

answered Jan 08 '21 at 14:31

Ronak Shah

377,200
20
156
213

How does this compare to using `enquo`? – slhck Jan 08 '21 at 14:32
I haven't used `enquo` enough to know about it. Additionally, both `deparse` and `substitute` are base R functions. – Ronak Shah Jan 08 '21 at 14:41

Turn a {{}} (dplyr double curly braces) interpolation into a string

2 Answers2

Linked