# Decision Tree

A Ruby library which implements [ID3 (information gain)](https://en.wikipedia.org/wiki/ID3_algorithm) algorithm for decision tree learning. Currently, continuous and discrete datasets can be learned.

- Discrete model assumes unique labels & can be graphed and converted into a png for visual analysis
- Continuous looks at all possible values for a variable and iteratively chooses the best threshold between all possible assignments. This results in a binary tree which is partitioned by the threshold at every step. (e.g. temperate > 20C)

## Features
- ID3 algorithms for continuous and discrete cases, with support for inconsistent datasets.
- [Graphviz component](http://rockit.sourceforge.net/subprojects/graphr/) to visualize the learned tree 
- Support for multiple, and symbolic outputs and graphing of continuous trees.
- Returns default value when no branches are suitable for input

## Implementation

- Ruleset is a class that trains an ID3Tree with 2/3 of the training data, converts it into a set of rules and prunes the rules with the remaining 1/3 of the training data (in a [C4.5](https://en.wikipedia.org/wiki/C4.5_algorithm) way).
- Bagging is a bagging-based trainer (quite obvious), which trains 10 Ruleset trainers and when predicting chooses the best output based on voting.

[Blog post with explanation & examples](http://www.igvita.com/2007/04/16/decision-tree-learning-in-ruby/)

## Example

```ruby
require 'decisiontree'

attributes = ['Temperature']
training = [
  [36.6, 'healthy'],
  [37, 'sick'],
  [38, 'sick'],
  [36.7, 'healthy'],
  [40, 'sick'],
  [50, 'really sick'],
]

# Instantiate the tree, and train it based on the data (set default to '1')
dec_tree = DecisionTree::ID3Tree.new(attributes, training, 'sick', :continuous)
dec_tree.train

test = [37, 'sick']
decision = dec_tree.predict(test)
puts "Predicted: #{decision} ... True decision: #{test.last}"

# => Predicted: sick ... True decision: sick

# Specify type ("discrete" or "continuous") in the training data
labels = ["hunger", "color"]
training = [
        [8, "red", "angry"],
        [6, "red", "angry"],
        [7, "red", "angry"],
        [7, "blue", "not angry"],
        [2, "red", "not angry"],
        [3, "blue", "not angry"],
        [2, "blue", "not angry"],
        [1, "red", "not angry"]
]

dec_tree = DecisionTree::ID3Tree.new(labels, training, "not angry", color: :discrete, hunger: :continuous)
dec_tree.train

test = [7, "red", "angry"]
decision = dec_tree.predict(test)
puts "Predicted: #{decision} ... True decision: #{test.last}"

# => Predicted: angry ... True decision: angry
```

## License

The [MIT License](https://opensource.org/licenses/MIT) - Copyright (c) 2006 Ilya Grigorik