code: def top_and_tail(a):
      
      if np.all(np.isnan(a)):
          return np.array([])
      nans = np.where(~np.isnan(a))[0]
      last = None if nans[-1]+1 == a.size else nans[-1]+1
      return a[nans[0]:last]
docs: Remove the NaNs from the top and tail (only) of a well log.
  
      Args:
          a (ndarray): An array.
      Returns:
          ndarray: The top and tailed array.