R - filling area to top of plot in ggplot2

Question

I am creating a plot in ggplot2 with filled densities, a few of which I would like to truncate. I apologize for lack of images--apparently I'm not allowed to post them yet. A simple example of beginning code:

dd = with(density(rnorm(100,0,1)),data.frame(x,y))

ylimit = .3

ggplot(data = dd, mapping = aes(x = x, y = y), geom="line") +
 layer(data = dd, mapping = aes(x = x, y = y), geom = "area", 
       geom_params=list(fill="red",alpha=.3)) +
         scale_x_continuous(limits = c(-3,3)) +
         scale_y_continuous(limits = c(0,ylimit))

This, however, results in an empty area in the middle of the filled density where dd$y > ylimit.

If I compensate for this with

dd$y = pmin(dd$y, ylimit)

The area is shaded but the plot displays an area slightly higher than ylimit, so the fill does not extend to the top of the graph.

Ideally I would like to know how to get ggplot display a plot exactly up to ylimit, but any other solutions for having the fill extend to the top of the plot would be welcome.

Edit:fixed the code.

This code does not work for me. Could you check it and edit? — John Colby
This link might also be useful to demonstrate the difference between "coord" and "scale" in ggplot2. had.co.nz/ggplot2/coord_cartesian.html — John Colby

John Colby John Colby · Accepted Answer · 2011-11-21T20:41:30

I think this is what you meant. Note the use of ifelse to get the truncating behavior.

dd = with(density(rnorm(100,0,1)), data.frame(x, y))

ylimit = .3

dev.new(width=4, height=4)
ggplot(data = dd, mapping = aes(x = x, y = y), geom="line") +
 layer(data = dd, mapping = aes(x = x, y = ifelse(y>ylimit, ylimit, y)), geom = "area", 
       geom_params=list(fill="red",alpha=.3)) +
         scale_x_continuous(limits = c(-3,3)) +
         coord_cartesian(ylim=c(0, ylimit))

enter image description here

R - filling area to top of plot in ggplot2

1 Answers