Class: KnnBall::Ball

Inherits:
Object
  • Object
show all
Defined in:
lib/knnball/ball.rb

Overview

This class represents a ball in the tree.

The value of this ball will be its center while its radius is the distance between the center and the most far sub-ball.

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(value, dimension = 1, left = nil, right = nil) ⇒ Ball

Returns a new instance of Ball.

Parameters:

  • value —

    the value associated to this ball

  • actual_dimension —

    the dimension used for sorting left and right tree



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# File 'lib/knnball/ball.rb', line 21

def initialize(value, dimension = 1, left = nil, right = nil)
  unless (value.respond_to?(:include?) && value.respond_to?(:[]))
    raise ArgumentError.new("Value must at least respond to methods include? and [].")
  end
  unless (value.include?(:point))
    raise ArgumentError.new("value must contains :point key but has only #{value.keys.inspect}")
  end
  @value = value
  @right = right
  @dimension = dimension
  @left = left
end

Instance Attribute Details

#dimension ⇒ Object

Returns the value of attribute dimension.



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# File 'lib/knnball/ball.rb', line 17

def dimension
  @dimension
end

#left ⇒ Object

Returns the value of attribute left.



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# File 'lib/knnball/ball.rb', line 17

def left
  @left
end

#right ⇒ Object

Returns the value of attribute right.



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# File 'lib/knnball/ball.rb', line 17

def right
  @right
end

#value ⇒ Object

Returns the value of attribute value.



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# File 'lib/knnball/ball.rb', line 17

def value
  @value
end

Instance Method Details

#center ⇒ Object 



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# File 'lib/knnball/ball.rb', line 34

def center
  value[:point]
end

#complete? ⇒ Boolean

Return true if this ball has a left and a right ball

Returns:

  • (Boolean) 


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# File 'lib/knnball/ball.rb', line 103

def complete?
  ! (@left.nil? || @right.nil?)
end

#count ⇒ Object 



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# File 'lib/knnball/ball.rb', line 91

def count
  1 + (left.nil? ? 0 : left.count) + (right.nil? ? 0 : right.count)
end

#distance(coordinates) ⇒ Object

Compute euclidien distance.

Parameters:

  • coordinates —

    an array of coord or a Ball instance



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# File 'lib/knnball/ball.rb', line 78

def distance(coordinates)
  coordinates = coordinates.center if coordinates.respond_to?(:center)
  Math.sqrt([center, coordinates].transpose.map {|a,b| (b - a)**2}.reduce {|d1,d2| d1 + d2})
end

#leaf? ⇒ Boolean

Retrieve true if this is a leaf ball.

A leaf ball has no sub_balls.

Returns:

  • (Boolean) 


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# File 'lib/knnball/ball.rb', line 98

def leaf?
  @left.nil? && @right.nil?
end

#nearest(target, min) ⇒ Object 



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# File 'lib/knnball/ball.rb', line 38

def nearest(target, min)
  result = nil
  d = [quick_distance(target), min[0]].min
  if d < min[0]
    min[0] = d
    result = self
  end
  
  # determine if we need to dive into sub tree
  dp = (center[dimension-1] - target[dimension-1]).abs
  new_result = nil
  if(dp < min[0])
    # must dive into both left and right
    unless(left.nil?)
      new_result = left.nearest(target, min)
      result = new_result unless new_result.nil?
    end
    unless right.nil?
      new_result = right.nearest(target, min)
      result = new_result unless new_result.nil?
    end
  else
    # only need to dive in one
    if(target[dimension-1] < center[dimension-1])
      unless(left.nil?)
        new_result = left.nearest(target, min)
      end
    else
      unless(right.nil?)
        new_result = right.nearest(target, min)
      end
    end
    result = new_result unless new_result.nil?
  end
  return result
end

#quick_distance(coordinates) ⇒ Object

Quickly compute a distance using Manhattan



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# File 'lib/knnball/ball.rb', line 84

def quick_distance(coordinates)
  distance(coordinates)
#      coordinates = coordinates.center if coordinates.respond_to?(:center)
#      [center, coordinates].transpose.map {|a,b| (b - a)**2}.reduce {|d1,d2| d1 + d2}
#      [center, coordinates].transpose.map {|a,b| (b - a).abs}.reduce {|d1,d2| d1 + d2}
end

#to_a ⇒ Object

Generate an Array from this Ball.

index 0 contains the value object, index 1 contains the left ball or nil, index 2 contains the right ball or nil.



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# File 'lib/knnball/ball.rb', line 112

def to_a
  if leaf?
    [@value, nil, nil]
  else
    [@value, (@left.nil? ? nil : @left.to_a), (@right.nil? ? nil : @right.to_a)]
  end
end

#to_h ⇒ Object

Generate a Hash from this Ball instance.

The generated instance contains keys :id, :left and :right



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# File 'lib/knnball/ball.rb', line 123

def to_h
  if leaf?
    {:value => @value, :left => nil, :right => nil} 
  else
    {:value => @value, :left => (@left.nil? ? nil : @left.to_h), :right => (@right.nil? ? nil : @right.to_h)}
  end
end