scoreSentiment = function(tab)

# function to get various sentiment scores, using the syuzhet package
scoreSentiment = function(tab)
{
 tab$syuzhet = get_sentiment(tab$Text, method="syuzhet")
 tab$bing = get_sentiment(tab$Text, method="bing")
 tab$afinn = get_sentiment(tab$Text, method="afinn")
 tab$nrc = get_sentiment(tab$Text, method="nrc")
 emotions = get_nrc_sentiment(tab$Text)
 n = names(emotions)
 for (nn in n) tab[, nn] = emotions[nn]
 return(tab)
}
 
# get the sentiment scores for the tweets
tweets = scoreSentiment(tweets)
tweets = tweets[tweets$TimeStamp < as.Date('19-04-2017', format = '%d-%m-%Y'),]