This is my personal .irbrc. It's fun.

.irbrc

class Object
  def self.interesting_methods
    self.public_methods.sort - Object.methods
  end

  def interesting_methods
    self.public_methods.sort - Object.methods
  end
end

class Array

  def average
    return 0 if self.length < 1
    return 0 if self.sum == 0
    self.sum.to_f/self.length.to_f
  end

  def round(places=0)
    self.map do |i|
      i.try(:round, places) || i
    end
  end

  def median(opts={})
    return nil if self.length < 1
    o = self.dup
    if opts[:round]
      if opts[:places].nil?
        opts[:places] = 0
      end
      o = self.round(opts[:places])
    end
    o.uniq!
    o.sort!

    return nil if o.length < 3

    i = (o.length / 2).round

    o[i]
  end

  def mode
    values = {}
    self.each do |score|
      score = score.round
      if values[score.to_s].nil?
        values[score.to_s] = 1
      else
        values[score.to_s] += 1
      end
    end
    values = values.sort_by{ |k, v| v }.to_h
    return 0 if values.keys.last.nil?
    values.keys.last.to_i
  end

end

module Enumerable
  def mean
    return self.sum / self.length.to_f
  end

  def median
    return nil if self.length < 1
    o = self.sort
    i = (self.length / 2).floor

    o[i]
  end

  def sample_variance
    m = self.mean
    sum = self.inject(0){|accum, i| accum + (i - m) ** 2 }
    return sum / (self.length - 1).to_f
  end

  def standard_deviation
    return Math.sqrt(self.sample_variance)
  end
end