This is a bubble sort in ruby code simple and explained here.

bubble_sort_in_ruby_simple_explained

# A method to define the bubble sort
def bubble_sort(array)
  # condition: When array has more than one element
  if array.count > 1
    swap = true
    # Loop: Run until swap is true
    while swap
      swap = false
      # Loop: Run loop with array counts and swap if 
      (array.length-1).times do |z|
        if array[z] > array[z+1]
          # swap if current number element is greater than next number element.
          array[z], array[z+1] =  array[z+1], array[z]
          # as we we have current number element is greater than next number element
          # so we updated more swap needed.
          swap = true
        end
      end
    end
    # While loop will stop once  array[z] > array[z+1] will be false 
    # then swap will become false line number 8.
  end
  array
end

print "Befor sort - #{[7,9,3,5,4,2,1]}"
print "\n"
print "After sort - #{bubble_sort([7,9,3,5,4,2,1])}"
print "\n"