R ggplot and facet grid: how to control x-axis breaks - r

Question

I am trying to plot the change in a time series for each calendar year using ggplot and I am having problems with the fine control of the x-axis. If I do not use scale="free_x" then I end up with an x-axis that shows several years as well as the year in question, like this:
If I do use scale="free_x" then as one would expect I end up with tick labels for each plot, and that in some cases vary by plot, which I do not want:
I have made various attempts to define the x-axis using scale_x_date etc but without any success. My question is therefore:
Q. How can I control the x-axis breaks and labels on a ggplot facet grid so that the (time series) x-axis is identical for each facet, shows only at the bottom of the panel and is in the form of months formatted 1, 2, 3 etc or as 'Jan','Feb','Mar'?
Code follows:
require(lubridate)
require(ggplot2)
require(plyr)
# generate data
df <- data.frame(date=seq(as.Date("2009/1/1"), by="day", length.out=1115),price=runif(1115, min=100, max=200))
# remove weekend days
df <- df[!(weekdays(as.Date(df$date)) %in% c('Saturday','Sunday')),]
# add some columns for later
df$year <- as.numeric(format(as.Date(df$date), format="%Y"))
df$month <- as.numeric(format(as.Date(df$date), format="%m"))
df$day <- as.numeric(format(as.Date(df$date), format="%d"))
# calculate change in price since the start of the calendar year
df <- ddply(df, .(year), transform, pctchg = ((price/price[1])-1))
p <- ggplot(df, aes(date, pctchg)) +
geom_line( aes(group = 1, colour = pctchg),size=0.75) +
facet_wrap( ~ year, ncol = 2,scale="free_x") +
scale_y_continuous(formatter = "percent") +
opts(legend.position = "none")
print(p)

Answer 1

here is an example:
df <- transform(df, doy = as.Date(paste(2000, month, day, sep="/")))
p <- ggplot(df, aes(doy, pctchg)) +
geom_line( aes(group = 1, colour = pctchg),size=0.75) +
facet_wrap( ~ year, ncol = 2) +
scale_x_date(format = "%b") +
scale_y_continuous(formatter = "percent") +
opts(legend.position = "none")
p
Do you want this one?
The trick is to generate day of year of a same dummy year.
UPDATED
here is an example for the dev version (i.e., ggplot2 0.9)
p <- ggplot(df, aes(doy, pctchg)) +
geom_line( aes(group = 1, colour = pctchg), size=0.75) +
facet_wrap( ~ year, ncol = 2) +
scale_x_date(label = date_format("%b"), breaks = seq(min(df$doy), max(df$doy), "month")) +
scale_y_continuous(label = percent_format()) +
opts(legend.position = "none")
p