[R] Changing X axis of ggplot

[Aren Cambre]

Thanks to Joshua Wiley for turning me on to ggplot2.

I am making a plot using this:
p <- ggplot(dallas, aes(x = offense_hour)) + geom_bar() + coord_polar()

Dallas is a data frame, and offense_hour is a column with chron
objects from the chron library. In this case, the chron object was
created with the times function. It is only a time (H:M:S) with no
date attached.

The plot shows up fine, but the X axis labels are 0.0 through 1.0. How
do I convert this to 0:00 through 23:59 (or whatever may be
appropriate given the breaks)?

My searches lead me to scale_x_discrete, but I am not clear if that's
even the right function.

Aren