TDD array assignment code partner project with Kyle

array_assignment.rb

#require 'Math'

class ArrayStatistic
  def initialize(array)
    @array = array
  end

  def largest
    @array.sort[-1]
  end

  def smallest
    @array.sort[0]
  end

  def average
    @array.inject(:+) / @array.size
  end

  def standard_deviation
    squared_differences = 0
    @array.each do |number|
      squared_differences += (number - average) ** 2
    end
    variance = squared_differences.to_f / @array.length
    Math.sqrt(variance)
  end

  def nth_smallest(number)
    @array.sort[number-1]
  end

  def sum
    @array.inject(:+)
  end

  def product
    @array.inject(:*)
  end

  def difference
    largest - smallest
  end

  def digit_frequency
    hash = {}
    @array.each do |number|
      digits = number.to_s.length.to_s
      if hash[digits].nil?
        hash[digits] = 1
      else
        hash[digits] += 1
      end
    end
    hash
  end

  def frequency
    hash = {}
    @array.each do |number|
      if hash[number.to_s].nil?
        hash[number.to_s] = 1
      else
        hash[number.to_s] += 1
      end
    end
    hash
  end

end