r - Remove a layer from a ggplot2 chart

Question

I'd like to remove a layer (in this case the results of geom_ribbon) from a ggplot2 created grid object. Is there a way I can remove it once it's already part of the object?

library(ggplot2)
dat <- data.frame(x=1:3, y=1:3, ymin=0:2, ymax=2:4)
p <- ggplot(dat, aes(x=x, y=y)) + geom_ribbon(aes(ymin=ymin, ymax=ymax), alpha=0.3) 
     + geom_line()

# This has the geom_ribbon
p

# This overlays another ribbon on top
p + geom_ribbon(aes(ymin=ymin, ymax=ymax, fill=NA))

I'd like this functionality to allow me to build more complicated plots on top of less complicated ones. I am using functions that return a grid object and then printing out the final plot once it is fully assembled. The base plot has a single line with a corresponding error bar (geom_ribbon) surrounding it. The more complicated plot will have several lines and the multiple overlapping geom_ribbon objects are distracting. I'd like to remove them from the plots with multiple lines. Additionally, I'll be able to quickly create alternative versions using facets or other ggplot2 functionality.

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Edit: Accepting @mnel's answer as it works. Now I need to determine how to dynamically access the geom_ribbon layer, which is captured in the SO question here.

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Edit 2: For completeness, this is the function I created to solve this problem:

remove_geom <- function(ggplot2_object, geom_type) {
  layers <- lapply(ggplot2_object$layers, function(x) if(x$geom$objname == geom_type) NULL else x)
  layers <- layers[!sapply(layers, is.null)]

  ggplot2_object$layers <- layers
  ggplot2_object
}

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Edit 3: See the accepted answer below for the latest versions of ggplot (>=2.x.y)

Answer 1

If you look at

p$layers
[[1]]
mapping: ymin = ymin, ymax = ymax 
geom_ribbon: na.rm = FALSE, alpha = 0.3 
stat_identity:  
position_identity: (width = NULL, height = NULL)

[[2]]
geom_line:  
stat_identity:  
position_identity: (width = NULL, height = NULL)

You will see that you want to remove the first layer

You can do this by redefining the layers as just the second component in the list.

p$layer <- p$layer[2]

Now build and plot p

p

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Note that p$layer[[1]] <- NULL would work as well. I agree with @Andrie and @Joran's comments regarding in wehat cases this might be useful, and would not expect this to be necessarily reliable.