The first think you need to do is to download tweets. You need to Setup your tweeter account. Much Information can be found in Internet on how to do it. The following two links were useful for my Setup (last checked in May 2017)

In particular I found the following two links useful (last checked in May 2017):

Link 1

Link 2

R Libraries

You will need the following R packages

library("devtools")
library("twitteR")
library("ROAuth")

Supposing you have your keys You have to run the following code

api_key <- XXXXXXXXXXXXXXXXXXXXXX
api_secret <- XXXXXXXXXXXXXXXXXXXXXX
access_token <- XXXXXXXXXXXXXXXXXXXXXX
access_token_secret <- XXXXXXXXXXXXXXXXXXXXXX


setup_twitter_oauth(api_key,api_secret)

Change XXXXXXXXXXXXXXXXXXXXXX to your keys (if you have Setup your tweeter account you know which keys I mean).

Let's now suppose we want to download tweets on coffee. The following code will do it

search.string <- "#coffee"
no.of.tweets <- 1000

c_tweets <- searchTwitter(search.string, n=no.of.tweets, lang="en") 

You will get 1000 tweets on "coffee".

Now we need to access the text of the tweets. So we do it in this way (we also need to clean up the tweets from special characters that for now we don't need, like emoticons with the sapply function.)

coffee_tweets = sapply(c_tweets, function(t) t$getText())

coffee_tweets <- sapply(coffee_tweets,function(row) iconv(row, "latin1", "ASCII", sub=""))

and you can check your tweets with the head function.

head(coffee_tweets)