Learning Data Mining with Python - Second Edition

n-gram features

One variation on the standard bag-of-words model is called the n-gram model. An n-grams model addresses the deficiency of context in the bag-of-words model. With a bag-of-words model, only individual words are counted by themselves. This means that common word pairs, such as United States, lose meaning they have in the sentence because they are treated as individual words.

There are algorithms that can read a sentence, parse it into a tree-like structure, and use this to create very accurate representations of the meaning behind words. Unfortunately, these algorithms are computationally expensive. This makes it difficult to apply them to large datasets.

To compensate for these issues of context and complexity, the n-grams ...