hey.rb

def revrot(str, size)
  if size > str.length or size == 0 
    ""
  else
    # Create an array of arrays of integers
    # Ex: str="1234567", size=3 results in [[1,2,3], [4,5,6], [7]]
    digit_groups = str.chars.map{|c| c.to_i }.each_slice(size).to_a
    
    # If `digit_groups` contains a last incomplete array
    # (`[7]` in the example above), remove it
    if str.length.to_f / size % 1 != 0
      digit_groups.delete_at(-1)
    end
    
    # Loop through `digit_groups`, operating on each `group` in sequence
    # In the example from above `group` will first be `[1,2,3]`, then
    # it will be `[4,5,6]`. The block (everything between `do` and `end`) will
    # run twice, because `digit_groups` has two elements in it.
    digit_groups.each do |group|
      # `result` determines which action to take
      result = group.reduce(:+).even?
      
      if result
        #do something
      else
        #do something else
      end
    end
  end
end