Class: Wallace::Utility::ScaledArray

Inherits:
Object
  • Object
show all
Defined in:
lib/utility/scaled_array.rb

Instance Method Summary collapse

Constructor Details

#initialize(items, probabilities) ⇒ ScaledArray

Returns a new instance of ScaledArray.



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# File 'lib/utility/scaled_array.rb', line 3

def initialize(items, probabilities)
  @items = items
  @cprob = []
  
  # Convert the probabilities into cumulative probabilities.
  sum = 0.0
  for p in probabilities
    @cprob << sum
    sum += p
  end
  
end

Instance Method Details

#sample ⇒ Object 



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# File 'lib/utility/scaled_array.rb', line 16

def sample
  point = Random.rand
  return self.select(point)
end

#select(point) ⇒ Object 



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# File 'lib/utility/scaled_array.rb', line 21

def select(point)
  
  # Initialise the lower and upper bounds of the binary search
  # at either end of the distribution.
  lb = 0
  ub = @items.length - 1
  
  # Keep searching until the upper and lower bound converge.
  until lb == ub
  
    # Select the point in between the lower and upper bound
    # as the pivot.
    pivot = lb + ((ub - lb) / 2)
    
    # If the point is less than the start of the area for
    # the pivot, move the upper bound back one.
    if point < @cprob[pivot]
      ub = pivot - 1
      
    # Check if the point lies within the bounds of the pivot.
    elsif pivot == ub or point < @cprob[pivot+1]
      lb = ub = pivot
      
    # If it doesn't, then move the lower bound forward.
    else
      lb = pivot + 1
    end
    
  
  end
  
  return @items[lb]
  
end

#select_old(point) ⇒ Object 



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# File 'lib/utility/scaled_array.rb', line 57

def select_old(point)

  # If there is only a single item in the distribution,
  # then return that item.
  return @items[0] if @items.length == 1
  
  # Initialise the lower and upper bounds of the binary search
  # at either end of the distribution.
  lb = 0
  ub = @items.length - 1
  
  # Keep searching until the upper and lower bound converge.
  until lb == ub
  
    # Select the point in between the lower and upper bound
    # as the pivot.
    pivot = lb + ((ub - lb) / 2)
  
    if point <= @cprob[pivot]
      ub = pivot
    else
      lb = pivot + 1
    end
    
  
  end
  
  return @items[pivot]
  
end