Decision trees

Decision trees are a class of supervised learning algorithms like a flow chart that consists of a sequence of nodes, where the values for a sample are used to make a decision on the next node to go to.  

The following example gives a very good idea of how decision trees are a class of supervised learning algorithms:

As with most classification algorithms, there are two stages to using them:

• The first stage is the training stage, where a tree is built using training data. While the nearest neighbor algorithm from the previous chapter did not have a training phase, it is needed for decision trees. In this way, the nearest neighbor algorithm is a lazy learner, only doing any work when it needs to make a prediction. In contrast, decision trees, like most classification methods, are eager learners, undertaking work at the training stage and therefore needing to do less in the predicting stage...