Class: Wallace::Koza::Builder::HalfBuilder

Inherits:
Wallace::Koza::Builder show all
Defined in:
lib/modules/koza/builder/half_builder.rb

Overview

The Half Builder is a (slightly modified) implementation of Koza’s Ramped Half-and-Half builder.

It works by selecting a random integer d, between the minimum and maximum depth inclusively. probability_grow of the time the grow method is used to generate a tree of up to depth d using the GROW builder. (1-probability_grow) of the time the FULL method is used to generate trees of exactly depth d.

Instance Attribute Summary collapse

Attributes inherited from Wallace::Koza::Builder

#depth_limits, #non_terminals, #terminals

Instance Method Summary collapse

Methods inherited from Wallace::Koza::Builder

#prepare

Constructor Details

#initialize(probability_grow, probability_terminal) ⇒ HalfBuilder

Constructs a new HalfBuilder.

Parameters:

  • probability_grow, the probability that the GROW method will be used when generating a tree.

  • probability_terminal, the probability that a terminal node will be built when using the GROW method.



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# File 'lib/modules/koza/builder/half_builder.rb', line 20

def initialize(probability_grow, probability_terminal)
  @probability_grow = probability_grow
  @probability_terminal = probability_terminal
end

Instance Attribute Details

#probability_grow ⇒ Object (readonly)

The probability that the GROW method will be used to generate a tree.



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# File 'lib/modules/koza/builder/half_builder.rb', line 10

def probability_grow
  @probability_grow
end

#probability_terminal ⇒ Object

The probability that a terminal will be selected when constructing a node using the GROW method.



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# File 'lib/modules/koza/builder/half_builder.rb', line 13

def probability_terminal
  @probability_terminal
end

Instance Method Details

#build_subtree(depth, opts = {}) ⇒ Object

Builds a new subtree of a maximum given depth using either the GROW or FULL method.

Parameters:

  • depth, the (maximum) depth of the subtree.

  • opts, a hash of keyword options for this method. -> random, the RNG to use for the process.



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# File 'lib/modules/koza/builder/half_builder.rb', line 49

def build_subtree(depth, opts = {})

  opts[:random] ||= Random.new

  return Wallace::Koza::Builder::GrowBuilder.grow_subtree(
    @terminals,
    @non_terminals,
    depth,
    @probability_terminal,
    random: opts[:random]
  ) if @probability_grow <= opts[:random].rand

  return Wallace::Koza::Builder::FullBuilder.full_subtree(
    @terminals,
    @non_terminals,
    depth,
    random: opts[:random]
  )

end

#build_tree(opts = {}) ⇒ Object

Builds a new Koza Tree of depth d, where d is within the allowed minimum and maximum tree depths, using either the GROW or FULL method.

Parameters:

  • opts, a hash of keyword options for this method. -> random, the RNG to use for the process.

Returns: A new Koza tree.



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# File 'lib/modules/koza/builder/half_builder.rb', line 39

def build_tree(opts = {})
  Wallace::Koza::KozaTree.new(build_subtree(@depth_limits.sample, random: opts[:random]))
end

#probability_full ⇒ Object

Returns the probability that the FULL method will be used to generate a tree.



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# File 'lib/modules/koza/builder/half_builder.rb', line 26

def probability_full
  1.0 - @probability_grow
end