docs: def calculate_mean_vectors(X, y):
      """Calculates the mean samples per class
      
      Parameters:
      -----------
      X : array-like, shape (m, n) - the samples
      y : array-like, shape (m, ) - the class labels
      
      Returns:
      --------
      mean_vectors : array-like, shape (k, )
      Those are the mean samples from each k classes.
      
      """
  
      return [np.mean(X[y == cl, :], axis=0) for cl in np.unique(y)]