stats.rb

# bunch of stats functions for quick usage in arrays... hobbled together from myself and a bunch of blogs... 
module Stats

  def sumitup
    if self.class == Hash
      sum = self.inject(0){|total, item| total = total + (item[1] || 0);  total}
    end
    if self.class ==  Array
      sum = self.inject(0){|total, item| total = total + (item || 0); total}
    end
    sum
  end
  
  def average
    the_sum = Float(sumitup ? sumitup : 0)
    the_length = Float(self.length)
    the_sum / the_length
  end
  
  def median
    numbers = self.class == Hash ? self.values : self 
    n = (numbers.length - 1) / 2 # Middle of the array
     n2 = (numbers.length) / 2 # Other middle of the array.
                                           # Used only if amount in array is even
      if numbers.length % 2 == 0 # If number is even
       median = (numbers[n] + numbers[n2]) / 2
      else
       median = numbers[n]
      end

      return median
  end
  
  def mode
    numbers = self.class == Hash ? self.values : self 
    c_n_count = 0 # Current number count
     length = numbers.length - 1
     amount = {} # New array for the number of times each number occurs in the array
      for x in 0..length
       c_number = numbers[x]
        for y in 0..length
          if numbers[y] == c_number # If the current number is
                                                   # equal to the upper level current number
           c_n_count = c_n_count + 1
          end
        end
       amount[x] = c_n_count # Add the total number of occurences in the value array
       c_n_count = 0
      end
     max = 0
     high_number = 0
      for x in 0..length
        if amount[x] > max # If the current number breaks the previous high record
         max = amount[x] # Reset the max to this new record
         high_number = x # Set the new most common number to that number
        end
      end

     return numbers[high_number]
  end
  
  def variance
      population = self.class == Hash ? self.values : self 
      n = 0
      mean = 0.0
      s = 0.0
      population.each { |x|
        n = n + 1
        delta = x - mean
        mean = mean + (delta / n)
        s = s + delta * (x - mean)
      }
      # if you want to calculate std deviation
      # of a sample change this to "s / (n-1)"
      return s / n
    end

    # calculate the standard deviation of a population
    # accepts: an array, the population
    # returns: the standard deviation
    def standard_deviation
      Math.sqrt(variance)
    end

end


class Array
    include Stats
end