Classifying text is used for a number of purposes:

• Spam detection
• Authorship attribution
• Sentiment analysis
• Age and gender identification
• Determining the subject of a document
• Language identification

Spamming is an unfortunate reality for most email users. If an email can be classified as spam, then it can be moved to a spam folder. A text message can be analyzed and certain attributes can be used to designate the email as spam. These attributes can include misspellings, lack of an appropriate email address for the recipients, and a non-standard URL.

Classification has been used to determine the authorship of documents. This has been performed on historical documents, such as The Federalist Papers and the book Primary Colors, where the authors were identified using classification techniques.

Sentiment analysis is a technique that determines the attitude...