agarie/measurable

module Measurable
  module Minkowski

    # call-seq:
    #     minkowski(u, v) -> Numeric
    #
    # Calculate the sum of the absolute value of the differences between each
    # coordinate of +u+ and +v+.
    #
    # Arguments:
    # - +u+ -> An array of Numeric objects.
    # - +v+ -> An array of Numeric objects.
    # Returns:
    # - The Minkowski (or L1) distance between +u+ and +v+.
    # Raises:
    # - +ArgumentError+ -> The sizes of +u+ and +v+ don't match.
    def minkowski(u, v)
      # TODO: Change this to a more specific, custom-made exception.
      raise ArgumentError if u.size != v.size

      u.zip(v).reduce(0) do |acc, elem|
        acc += (elem[0] - elem[1]).abs
      end
    end

    def self.extended(base) # :nodoc:
      base.instance_eval do
        alias :cityblock :minkowski
        alias :manhattan :minkowski
      end
      super
    end

    def self.included(base) # :nodoc:
      base.class_eval do
        alias :cityblock :minkowski
        alias :manhattan :minkowski
      end
      super
    end
  end

  extend Measurable::Minkowski
end