array_helpers.rb

# This kata is designed to test your ability to extend the functionality of built-in classes. In this case, we want you to extend the built-in Array class with the following methods: square(), cube(), average(), sum(), even() and odd().

# Explanation:

# square() must return a copy of the array, containing all values squared
# cube() must return a copy of the array, containing all values cubed
# average() must return the average of all array values; on an empty array must return NaN (note: the empty array is not tested in Ruby!)
# sum() must return the sum of all array values
# even() must return an array of all even numbers
# odd() must return an array of all odd numbers
# Note: the original array must not be changed in any case!

# E.g.
# numbers = [1, 2, 3, 4, 5]

# numbers.square()  # must return [1, 4, 9, 16, 25]
# numbers.cube()    # must return [1, 8, 27, 64, 125]
# numbers.average() # must return 3
# numbers.sum()     # must return 15
# numbers.even()    # must return [2, 4]
# numbers.odd()     # must return [1, 3, 5]

class Array
    def square()
        map { |x| x ** 2 }
    end
  
    def cube()
        map { |x| x ** 3 }
    end
  
    def average()
        inject(0.0) { |sum, x| sum + x } / self.size
    end
  
    def sum()
        reduce(:+)
    end
  
    def even
        select { |x| x.even? }
    end
  
    def odd
        select( { |x| x.odd? })
    end
  end

  array = [1, 2, 3, 4, 5]
  p array.square()
  p array.cube()
  p array.average()
  p array.sum()
  p array.even()
  p array.odd()

  test_arr = []
  p test_arr.average()