40 Algorithms Every Programmer Should Know

Document categorization

Unsupervised machine learning algorithms can also be applied to a repository of unstructured textual data—for example, if we have a dataset of PDF documents, then unsupervised learning can be used to do the following:

• Discover various topics in the dataset

• Associate each PDF document to one of the discovered topics

This use of unsupervised learning for document classification is shown in the following figure. This is another example in which we are adding more structure to unstructured data:

Figure 6.4: Using unsupervised learning for document classification

Note that, in this case, unsupervised learning suggests ...