library(ggplot2)

tweets <- read.csv(url("http://s3.amazonaws.com/cgcdn-misc/tweets_hillary.csv"))
tweets$hours_est <- as.numeric(format(as.POSIXct(tweets$created_at, format="%Y-%m-%d %H:%M", tz = "UTC")-14400, format="%H"))
ggplot(tweets[tweets$source!="Thunderclap",], aes(x=hours_est, fill=source)) + geom_bar(position='dodge')