core_arithmetic.rb

class DataSet < Array

  def input(data)
    if data.kind_of?(Enumerable)
      data.each do |item|
        if item.kind_of?(Numeric) == true
          self << item
        else
          self.input(item)
        end
      end
    elsif data.kind_of?(Numeric)
      self << data
    else
      begin
        raise RuntimeError
      rescue
        puts "is the data numerable?"
      end
    end
  end
end

## need to extend the Array class in order to perform basic math. Otherwise,
#  the methods tend to crash as they attempt to run on Array instances.

class Array

  def sum
    self.inject(0) do |a,x|
      a + x
    end
  end

  def average
    self.sum.to_f / self.size
  end

  def median
    case self.size % 2
      when 0 then self.sort[self.size/2-1,2].average
      when 1 then self.sort[self.size/2].to_f
    end if self.size > 0
  end

end