twitteR is an R package which provides access to the Twitter API. Most functionality of the API is supported, with a bias towards API calls that are more useful in data analysis as opposed to daily interaction.
install.packages("twitteR")or use the github version. To do the latter:
install.packages(c("devtools", "rjson", "bit64", "httr"))
setup_twitter_oauth("API key", "API secret")
API secretare from the Twitter app page above. This will lead you through
httr's OAuth authentication process. I recommend you look at the man page for
httrfor an explanation of how it handles caching.