Training decision trees

Let's create a decision tree using an algorithm called Iterative Dichotomiser 3(ID3). Invented by Ross Quinlan, ID3 was one of the first algorithms used to train decision trees. Assume that you are tasked with classifying animals as cats or dogs. Unfortunately, you cannot observe the animals directly and must use only a few attributes of the animals to make your decision. For each animal, you are told whether or not it likes to play fetch, whether or not it is frequently grumpy, and its favorite of three types of food.To classify new animals, the decision tree will examine a featureat each node. The edge it follows to the next node will depend on the outcome of the test. For example, the first node might ask whether or not the animal likes to play fetch. If the animal does, we will follow the edge to the left child node; if not, we will follow the edge to the right child node. Eventually an edge will connect to a leaf node that indicates whether the animal is a cat...