Warning when unsetting an aesthetic that's not used by a geom

[wch]

If you add a geom that uses a different data set, and it does not use an aesthetic set in the ggplot() call,

In the example below, I'm adding a geom_linerange() which uses a different data set from the one specified in the ggplot() call. The linerange doesn't have a y aesthetic. Its data set, d2, also doesn't have the yval column which was used in the aesthetic mapping for y at the top level.

If I map aes(y=NULL) in the geom_linerange, it gives a warning that it's ignoring y. If I don't map y, then it errors because it still tries to evaluate the y=yval mapping even though it's not used for that geom.

library(ggplot2)

d <- data.frame(
  xval = 1:2,
  yval = 1:2
)

d2 <- data.frame(
  xval = 3:4,
  yval2 = 3:4
)

p <- ggplot(d, aes(x=xval, y=yval)) +
  geom_point()

p + geom_linerange(aes(y = NULL, ymin = yval2, ymax = yval2+1), data = d2)
#> Warning: Ignoring unknown aesthetics: y

p + geom_linerange(aes(ymin = yval2, ymax = yval2+1), data = d2)
#> Error in eval(expr, envir, enclos) : object 'yval' not found

[hadley]

Hmmm, maybe it should not warn for aesthetics set to NULL?

[wch]

Is it possible to have it not try to evaluate the unused aesthetic? I think that would be preferable.

[hadley]

I don't see how that work work and still preserve the intent of flagging problems like aes(colur = blah)

[andbarker]

+1 for not warning when the aes is null.
Mainly because it forces you to explicitly stated when there's a dummy aes.

[hadley]

@wch maybe I misunderstood your question - there's no need to evaluate the aesthetics because identical(quote(NULL), NULL) is TRUE.