Can I use NLTK to determine if a comment is a positive one or a negative one?

Question

Can you show me a simple example using http://www.nltk.org/code to determine if a string about a happy or upset mood?

Answer 1

Nopey.

This is a task far beyond the capabilities of NLTK or any grammatical parser that is known or can be realistically imagined. Look at the NLTK Book to see what sorts of tasks it can accomplish which are far, far from your stated purpose.

As a cheap example:

I really enjoyed using your paper to train my dog.

Parse that up with NLTK and you can get

[('I', 'PRP'), ('really', 'RB'), ('enjoyed', 'VBD'), 
 ('using', 'VBG'), ('your', 'PRP$'), ('paper', 'NN'), 
 ('to', 'TO'), ('train', 'VB'), ('my', 'PRP$'), ('dog', 'NN')]

Where the parse tree would tell me that 'enjoyed' is the central (past-tense) verb of the simple sentence. To enjoy something is good. To train something is generally a good thing. Gerunds, nouns, comparatives, and such are relatively neutral. So give this a Good score of 0.90.

Except I really mean that I either hit my dog with your paper or let it excrete on the paper which you'd probably consider a not Good thing.

Hire a person for this recognition task.

Added for those who imagine that even trained classifiers are of much use:

Classify this real entry from a real customer review corpus using any classifier you like trained on any dataset you like:

This camera keeps on autofocussing in auto mode with a buzzing sound which can't be stopped. It would be really good if they have given an option to stop this autofocussing. If you want to have the date and time on the image, it's only through their software which reads the image's date and time from the image's meta-data. So if you use your card reader and copy images - you got to once again open them through their software to put the date and time. In that too, there isn't a direct way to add date and time - you got to say 'print images' to a different directory in which there is an option to specify the date and time . Even the slightest of the shakes totally distorts your image. Indoor images weren't so clear. You got to have flash 'on' to get it even though your room is well lit. The lens cap is a really annoying. the movie clips taken will always have some 'noise' in it - you can't avoid that.

The worst mood classification I obtained was "totally equivocal" yet humans can easily determine that this is anything but complimentary. This wasn't a randomly picked datum, rather one that was selected for negative bias without "hate" or "suxz" or similar.