Tidyeval splice operator !!! fails with ggplot's aes

问题

The article discussing tidy evaluation in ggplot2 gives the impression that aes() now supports quasiquoation. However, I'm having problems getting it to work with the unquote-splice operator !!!.

library( ggplot2 )

## Predefine the mapping of symbols to aesthetics
v <- rlang::exprs( x=wt, y=mpg )

## Symbol-by-symbol unquoting works without problems
ggplot( mtcars, aes(!!v$x, !!v$y) ) + geom_point()

## But unquote splicing doesn't...
ggplot( mtcars, aes(!!!v) ) + geom_point()
# Error: Can't use `!!!` at top level
# Call `rlang::last_error()` to see a backtrace

(Perhaps unsurprisingly) The same thing happens if the aesthetic mapping is moved to the geom:

ggplot( mtcars ) + geom_point( aes(!!v$x, !!v$y) )   # works
ggplot( mtcars ) + geom_point( aes(!!!v) )           # doesn't

Am I missing something obvious?

回答1:

That's because aes() takes x and y arguments and !!! only works within dots. We'll try to solve this particular problem in the future. In the interim you'll need to unquote x and y individually, or use the following workaround:

aes2 <- function(...) {
  eval(expr(aes(!!!enquos(...))))
}

ggplot(mtcars, aes2(!!!v)) + geom_point()

来源：https://stackoverflow.com/questions/55815963/tidyeval-splice-operator-fails-with-ggplots-aes