text: #!/usr/bin/env python3
  
  import numpy as np
  
  
  def normalizeRatings(Y, R):
      #NORMALIZERATINGS Preprocess data by subtracting mean rating for every 
      #movie (every row)
      #   [Ynorm, Ymean] = NORMALIZERATINGS(Y, R) normalized Y so that each movie
      #   has a rating of 0 on average, and returns the mean rating in Ymean.
      #
  
      m, n = Y.shape
      Ymean = np.zeros(m)
      Ynorm = np.zeros(Y.shape)
      for i in range(m):
          idx = R[i, :] == 1
          Ymean[i] = np.mean(Y[i, idx])
          Ynorm[i, idx] = Y[i, idx] - Ymean[i]
      #end
  
      return Ynorm, Ymean
      #end
  