# What Is Decision Tree in Data Structure?

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Heather Bennett

A decision tree is a widely used data structure in computer science and machine learning. It is a flowchart-like structure that represents decisions and their possible consequences. In simple terms, it is a tree-shaped model of decisions and their possible outcomes.

## Structure of a Decision Tree

A decision tree consists of nodes and edges. The nodes represent the decisions or test conditions, while the edges represent the possible outcomes or consequences of those decisions.

### Root Node

The root node is the topmost node in the decision tree. It represents the initial decision or test condition that leads to further branches.

### Internal Nodes

Internal nodes are the intermediate nodes between the root node and the leaf nodes. They represent subsequent decisions or test conditions based on which further branches are created.

### Leaf Nodes

Leaf nodes are the terminal nodes in a decision tree. They represent the final outcomes or consequences of all previous decisions or test conditions.

## How Does a Decision Tree Work?

To understand how a decision tree works, let’s consider an example:

• Hypothesis: Predict whether a customer will purchase a product based on their age and income.
• Data:
• Data Point 1: Age = 25, Income = \$40,000, Purchase = Yes
• Data Point 2: Age = 35, Income = \$60,000, Purchase = No
• Data Point 3: Age = 45, Income = \$80,000, Purchase = Yes
• Data Point 4: Age = 30, Income = \$50,000, Purchase = Yes
• Data Point 5: Age = 20, Income = \$30,000, Purchase = No

Based on this data, the decision tree can be constructed as follows:

### Step 1: Select the Root Node

The root node is selected based on the initial test condition. In this case, let’s choose the test condition of age < 30.

### Step 2: Create Branches from the Root Node

The root node is connected to two branches: one for age < 30 and another for age >= 30. These branches represent the possible outcomes of the initial test condition.

### Step 3: Add Internal Nodes and Leaf Nodes

For each branch created in Step 2, add internal nodes and leaf nodes based on subsequent test conditions and their outcomes. The process continues until all data points are classified.

In our example:

• Branch for age < 30:
• Internal Node: Test condition – income < \$50,000
• Leaf Node: Purchase = No (Data Point 5)

• Internal Node: Test condition – income >= \$50,000
• Leaf Node: Purchase = Yes (Data Point 1)
• Leaf Node: Purchase = Yes (Data Point 4)

• Branch for age >= 30:
• Leaf Node: Purchase = No (Data Point 2)
• Leaf Node: Purchase = Yes (Data Point 3)

The decision tree can be visualized as follows:

```          Age < 30?
/        \
No         Yes
/             \
Income < \$50k?   Purchase = Yes
/       \
No        Yes
/
Purchase = No
```

A decision tree is a powerful data structure that can be used for classification, regression, and other predictive tasks. It provides a clear and interpretable representation of decision-making processes based on given data.

In conclusion, a decision tree is a fundamental data structure in computer science and machine learning. It allows us to represent decisions and their outcomes in a structured and organized manner. By following the branches of the tree, we can make predictions or classifications based on given input parameters.

If you want to learn more about decision trees or how to implement them in different programming languages, check out our other tutorials!