listtest.rb

def relative_position(item, array)
    # returns a value between 1 and -1
    # 1 for first item, 0 for last item
    # equal distances between items
    if array.size <= 1
      return 0
    elsif array.size.odd?
      median = array.size / 2
      increment = 1.0 / median
      value = (array.index(item) - median) * (- increment)
      value
    else
      increment = 2.0 / (array.size - 1)
      value = 1 - (array.index(item) * increment)
    end
  end

  def relative_diff(item, array1, array2)
    # calculates the difference of index between item in two arrays
    # if item not in one array, gives the index in the other
    # if item not in any array, returns 0
    if array1.include?(item) && array2.include?(item)
      return (relative_position(item, array1) - relative_position(item, array2)).abs
    elsif array1.include?(item)
      return relative_position(item, array1)
    elsif array2.include?(item)
      return relative_position(item, array2)
    else
      return nil
    end
  end

  def euclidean_distance(array1, array2)
    # gives the vector distance of two arrays
    # item is axis, index is value
    if array1 & array2 == []
      return nil
    else
      all_distances = []
      array1.each do |item|
        # calculates distance for all items in array 1
        distance = relative_diff(item, array1, array2)
        all_distances << distance
      end
      (array2 - array1).each do |item|
        distance = relative_diff(item, array1, array2)
        all_distances << distance
      end
      sum_of_squared_distances = 0
      all_distances.each do |distance|
        sum_of_squared_distances += distance**2
      end
      return Math.sqrt(sum_of_squared_distances)
    end
  end

  def relevance(array1, array2)
    distance = euclidean_distance(array1, array2)
    intersection_size = (array1 & array2).size
    unless distance == nil
      relevance = intersection_size / distance
      return relevance
    end
    return nil
  end