How to rotate a matrix 90 degrees in Ruby

rotate_a_matrix_90_degrees.rb

#
# Transpose a matrix
# Make [[1,2,3], [4,5,6], [7,8,9]] becomes [[1,4,7], [2,5,8], [3,6,9]]
#
class Array
  def my_transpose
    size.times do |i|
      0.upto(i) do |j|
        self[i][j], self[j][i] = self[j][i], self[i][j]
      end
    end
    self
  end
end

#
# Reverse array
# Make [1,4,7] becomes [7,4,1]
#
def my_reverse(array)
  reverse = []
  i = -1

  array.each do
    reverse << array[i]
    i -= 1
  end

  reverse
end

#
# Rotate matrix 90
#
def rotate90(array)
  array = array.my_transpose
  array.map { |row| my_reverse(row) }
end

rotate90([[1, 2, 3], [4, 5, 6], [7, 8, 9]])
rotate90([[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12], [13, 14, 15, 16]])

#
# IRB console:
#
2.5.1 :1736 > rotate90([[1, 2, 3], [4, 5, 6], [7, 8, 9]])
 => [[7, 4, 1], [8, 5, 2], [9, 6, 3]] 
2.5.1 :1737 > rotate90([[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12], [13, 14, 15, 16]])
 => [[13, 9, 5, 1], [14, 10, 6, 2], [15, 11, 7, 3], [16, 12, 8, 4]]