code: def mean(x):
      
      if x.ndim > 1 and len(x[0]) > 1:
          return np.mean(x, axis=1)
      return x
docs: Return a numpy array of column mean.
      It does not affect if the array is one dimension
  
      Parameters
      ----------
      x : ndarray
          A numpy array instance
  
      Returns
      -------
      ndarray
          A 1 x n numpy array instance of column mean
  
      Examples
      --------
      >>> a = np.array([[1, 2, 3], [4, 5, 6], [7, 8, 9]])
      >>> np.array_equal(mean(a), [2, 5, 8])
      True
      >>> a = np.array([1, 2, 3])
      >>> np.array_equal(mean(a), [1, 2, 3])
      True