Learning Predictive Analytics with Python

Understanding the mathematics behind decision trees

The main goal in a decision tree algorithm is to identify a variable and classification on which one can give a more homogeneous distribution with reference to the target variable. The homogeneous distribution means that similar values of the target variable are grouped together so that a concrete decision can be made.

Homogeneity

In the preceding example, the first goal would be to find a parameter (out of four: Terrain, Rainfall, Groundwater, and Fertilizers) that results in a better homogeneous distribution of the target variable within those categories.

Without any parameter, the count of harvest type looks as follows:

Bumper	Moderate	Meagre
4	9	7

Let us calculate, for each parameter, ...