Colour lines by mean of value pairs in ggplot2

Question

When mapping colour to lines in ggplot2, e.g.:

x = data.frame(x = 1:6, y = c(0,0,10,10,0,0))
ggplot(x, aes(x, y, col=y)) + geom_line(size=5)

.. the lines colours are mapped to the first data point of each line segment. Is there any easy way to get ggplot to calculate the mean value of both points instead (ie. so the sloping lines are both scaled to the colour for 5)?

Answer 1

Similar idea as @Richard, but use the zoo package.

library(zoo)
x = data.frame(x = 1:6, y = c(0,0,10,10,0,0))
ggplot(x, aes(x, y, col=rollmean(y, 2, fill = 0))) + geom_line(size=5)