Algorithm to determine how positive or negative a statement/text is

Question

I need an algorithm to determine if a sentence, paragraph or article is negative or positive in tone... or better yet, how negative or positive.

For instance:

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Answer 1

There are many machine learning approaches for this kind of Sentiment Analysis. I used most of the machine learning algorithms, which are already implemented. my case I have used

weka classification algorithms

• SVM
• naive basian

• J48

  Only you have to do this train the model to your context , add featured vector and rule based tune up. In my case I got some (61% accuracy). So We move into stanford core nlp ( they trained their model for movie reviews) and we used their training set and add our training set. we could achieved 80-90% accuracy.