by Yanchang Zhao, RDataMining.com
There is a nice example on sentiment analysis with R at <http://viksalgorithms.blogspot.com.au/2012/06/tracking-us-sentiments-over-time-in.html>.
In the example, the Wikileaks cable corpus is analyzed to track US sentiments of other countries and their presidents over time. The example describes how to map sentences to a sentiment score of -5 to 5 with the AFINN list. It also introduces named entity recognition with the JRC-Names word list. Moreover, it uses random indexing technique to build up a matrix of topic words and sentiment words.
It is a good example to learn from to start your own sentiment analysis.