Using Enumerable to make standard iterators available to modify iterators

Question

I am Attempting to Use the Enumerable mixin to make all the standard iterators available in my class named NumberArray . From that I'm trying to use the inject iterator to get the average of odd numbers in the array .

My code looks like this

 class NumberArray
  include Enumerable
  def initialize
    @numbers = Array.new
  end

then @numbers array is then filled with 1000 numbers

and finally I'm trying to create my own inject iterator to get the average of the odd values.

def inject

    puts self.inject{|sum,x| sum = sum + x if sum mod 2 == 1}

    asum
  end

I am very new to Ruby.

Answer 1

You could also just subclass Array and override methods you want:

class NumberArray < Array
  def inject
    odds = select(&:odd?)
    odds.inject(:+).to_f / odds.size
  end
end

a = NumberArray.new([1,2,3,4,5])
a.inject # => 3.0

If it makes any sense to do it this way is another thing, but that's what you asked :)

Answer 2

Classes that use the Enumerable mixin must have an each method, which yields for each successive element.

Since your class NumberArray is backed by a normal array, you can use the array's each method:

class NumberArray
  # ...
  def each
    @numbers.each
  end
end

As for your inject method, when you call self.inject, it just calls the method you're currently in again. This is called recursion, and will cause a SystemStackError in this case. I also don't recommend redefining the inject method in NumberArray, because it will override the Enumerable implementation of inject.

I'd use a more descriptive method name like odd_avg:

def odd_avg
  odds = @numbers.select(&:odd?)
  odds.inject(:+).to_f / odds.size
end

The first line of this method gets all the odd elements from @numbers and puts it into odds. The next line first gets the sum of odds, then converts the sum to a float, then divides by the number of odds.