code: def safe_vstack(Xs):
      if any(sp.issparse(X) for X in Xs):
          return sp.vstack(Xs)
      else:
          return np.vstack(Xs)
  
imports: from __future__ import division, print_function
  from math import sqrt
  import warnings
  import numbers
  import numpy
  import scipy.sparse
  from ..base import BaseEstimator, TransformerMixin
  from ..utils import check_random_state, check_array
  from ..utils.extmath import randomized_svd, safe_sparse_dot, squared_norm
  from ..utils.extmath import fast_dot
  from ..utils.validation import check_is_fitted, check_non_negative
  from ..utils import deprecated
  from ..exceptions import ConvergenceWarning
  from .cdnmf_fast import _update_cdnmf_fast
label_desc: Use image node_id 1 for calling a global function with example usage: safe_vstack(Xs) and returns: sp, np