Temporarily disable aesthetics already defined in ggplot()

Question

We may want to define some global aes() for a ggplot() graphics, but exclude them in some layers. For instance suppose the following example:

foo <- data.frame(x=runif(10),y=runif(10))
bar <- data.frame(x=c(0,1),ymin=c(-.1,.9),ymax=c(.1,1.1))
p <- ggplot(foo,aes(x=x,y=y))+geom_point()

Everything is good. However when trying to add the ribbon:

p <- p + geom_ribbon(data=bar, aes(x=x,ymin=ymin,ymax=ymax), alpha=.1)
# Error: Discrete value supplied to continuous scale

This error happens because we have already defined y as a part of global aes() that applies also to the geom_ribbon(), but the bar does not have it.

I have found two possibilities to escape this error, one of them is to remove y=y from the original ggplot(foo,aes(x=x,y=y)), however every time in the future I need to draw something I should add y=y to the aes() that is not good.

The other possibility is to add a fake y column to bar:

bar = cbind(bar, y=0)
p <- p + geom_ribbon(data=bar, aes(x=x,ymin=ymin,ymax=ymax), alpha=.1)

Now works good. However I don't like acting so, as it's a fake variable. Is there any way to temporarily disable the already defined aes() in ggplot() when calling the geom_ribbon()?

Answer 1

As said in the comments by @ErnestA, we can unmap the aesthetics by setting them to NULL

      aes(y=NULL,x=x,ymin=ymin,ymax=ymax)

PS: For the legend you can now override aesthetic by aes.override