Drupal commit message mentions by month

library(ggplot2)
library(scales)
library(plyr)

df <- read.csv("http://dl.dropbox.com/u/361076/d8contrib.csv")
df$month <- format(as.Date(df$date), format = "%y-%m")
# Get a total count of all contributions
df$datetime <- as.Date(df$date)
df <- ddply(df, .(contributor), transform, count = length(contributor))
# Filter out users with less than 20.
df <- df[df$count > 20, ]

ggplot(df, aes(datetime, fill = contributor)) + geom_histogram() + opts(legend.position = "none") + 
    scale_x_date(breaks = "1 month", labels = date_format("%m-%y")) + facet_wrap(~contributor, 
    ncol = 1)